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This file describes the BASH debugger, the BASH symbolic debugger.
This is the 3.1-0.06 Edition, 23 July 2006, for BASH.
Copyright (C) 2002, 2003, 2004, 2006 Rocky Bernstein
| 1. Summary of the BASH Debugger | Overview of Debugger with a sample session | |
| 2. Getting in and out | ||
| 3. Script Setup inside the BASH Debugger | Script setup inside the BASH debugger | |
| 4. BASH Debugger Command Reference | BASH debugger command reference | |
| 5. Using the BASH debugger from a front-end user interface | Using the Debugger from a front-end user interface | |
| 6. Reporting Bugs | Reporting bugs | |
| 7. History and Acknowledgments | ||
Appendices |
||
| A. GNU GENERAL PUBLIC LICENSE | GNU General Public License says how you can copy and share bashdb | |
| B. GNU Free Documentation License | The license for this documentation | |
Indexes (nodes containing large menus) |
||
| Function Index | An item for each function name. | |
| Command Index | An item for each command name. | |
| Variable Index | An item for each documented variable. | |
| General Index | An item for each concept. | |
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The purpose of a debugger such as the BASH debugger going on "inside" a bash script while it executes.
the BASH debugger these) to help you catch bugs in the act:
Although you can use the BASH debugger to debug scripts written in BASH, it can also be used just as a front-end for learning more about programming in BASH. As an additional aid, the debugger can be used within the context of an existing script with its functions and variables that have already been initialized; fragments of the existing can be experimented with by entering them inside the debugger.
| 1.1 A Sample BASH Debugger Session | A Sample BASH Debugger session | |
| 1.2 Interactive Line Tracing Session | ||
| Free software | Freely redistributable software |
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You can use this manual at your leisure to read all about the BASH debugger. However, a handful of commands are enough to get started using the debugger. This chapter illustrates those commands.
Below we will debug a script that contains a function to compute the factorial of a number: fact(0) is 1 and fact(n) is n*fact(n-1).
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The command invocation uses the option "-L ." Here we assume that the bashdb script and the debugger files are in the
same location. If you are running from the source code, this will be the case. However if bashdb has been installed this probably won't
be true and here you probably don't need to use "-L ." Instead you would type simply bashdb /tmp/fact.sh.
Position information consists of a filename and line number, e.g. (/tmp/fact.sh:9) and is given parenthesis. This position
format is similar to that used by the Perl debugger and is also in the same format used by my GNU make debugger (
http://bashdb.sourceforge.net/remake. and Extended python debugger
http://remake.sourceforge.net/pydb. GNU Emacs and DDD can parse this
and in fact the same regular expression is used on the 3 debuggers.
The first debugger command we gave -, we listed a window of lines before where we were executing. Because the window, 10 lines, is larger than the number of lines to the top of the file we printed only 9 lines here. The next command list starting from the current line and again wants to print 10 lines but because there are only one remaining line, that is what is printed.
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Ooops... The variable n isn't initialized.
The first step command steps the script one instruction. It may seem odd that the line printed is exactly the same one as before. What has happened though is that we've "stepped" into the subshell needed to run `fact 0`; we haven't however started running anything inside that subshell yet though.
To indicate that which piece of the multi-part line echo fact 0 is: `fact 0` we show that part all by itself fact
0. If nothing is shown then it means we are running the beginning statement or in this case the outermost statement.
To indicate that we are now nested in a subshell, notice that the command number, starting with 3, or the third command entered, now appears in parenthesis. Each subshell nesting adds a set of parenthesis.
The first step command steps the script one instruction; it didn't advance the line number, 9, at all. That is because
we were stopping before the command substitution or backtick is to take place. The second command we entered was just hitting the return
key; bashdb remembers that you entered step previously, so it runs the step rather than next, the other alternative
when you hit RET. Step one more instruction and we are just before running the first statement of the function.
Next, we print the value of the variable n. Notice we need to add a preceding dollar simple to get the substitution or value of n. As we will see later, if the pe command were used this would not be necessary.
We now modify the file to add an assignment to local variable n and restart.
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This time we use the list debugger command to list the lines in the file. From before we know it takes three steps
commands before we get into the fact() function, so we add a count onto the step command. Notice we abbreviate step
with s; we could have done likewise and abbreviated list with l.
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Again we just use RET to repeat the last step commands. And again the fact that we are staying on the same
line 4 means that the next condition in the line is about to be executed. Notice that we see the command (echo 1 or
return) listed when we stay on the same line which has multiple stopping points in it. Given the information above, we
know that the value echo'ed on return will be 1.
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We saw that we could step with a count into the function fact(). However above took another approach: we set a stopping point or
"breakpoint" at line 5 to get us a little ways into the fact() subroutine. Just before line 5 is to executed, we will get back into
the debugger. The continue command just resumes execution until the next stopping point which has been set up in some way.
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In addition to listing by line numbers, we can also list giving a function name. Below, instead of setting a breakpoint at line 5 and running "continue" as we did above, we try something slightly shorter and slightly different. We give the line number on the "continue" statement. This is a little different in that a one-time break is made on line 5. Once that statement is reached the breakpoint is removed.
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When we stop at line 5 above, we have already run fact(0) and output the correct results. The output from the program "fact 0 is:
1" is intermixed with the debugger output. The T command above requests call stack output and this confirms that we are
not in the fact(0) call but in the fact(3) call. There are 4 lines listed in the stack trace even though there is just one call from
the main program. The top line of the trace doesn't really represent a call, it's just where we currently are in the program. That last
line is an artifact of invoking bash from the bashdb script rather than running bash --debugger.
The last message in the output above `Debugged program exited normally.' is from the BASH debugger;
it indicates script has finished executing. We can end our bashdb session with the bashdb quit command.
Above we did our debugging session on the command line. If you are a GNU Emacs user, you can do your debugging inside that. Also there is a(nother) GUI interface called DDD that supports the BASH debugger.
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One of the things I've always found annoying about set -x tracing is that there is no position information given in
the trace output, in particular the line number and the file name. Although function nesting information is shown, other important Information
such as BASH shell and subshell nesting count is not. From a programming standpoint, these are just as important because
they affect the namespace, or the scope over which variables are seen.
Although I this is best fixed inside BASH, the debugger provides a means for showing position information when tracing a script. Here's a simple session.
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An explanation of the output. The level is how many invocations of BASH are in effect before the statement
shown is executed. The subshell is how many subshells you are nested in. Subshells are used by command substitution--`..'
and $(...)--as well as arithmetic expressions ((...)). The depth is the function depth or how many
calls you are nested in. A "source" command also increases this depth.
Notice also that in contrast to set -x tracing, the line shown is exactly as you entered it in the source. So if you
indented statements in a meaningful way, it will help you understand the statement nesting level. But as before, if a line contains
multiple statements, you are not executing the first statement in the line and set showcommand is not turned off
(by default it is on), that statement is shown in addition below the multi-statement line. Such an example can be seen right at the
beginning where fact 0 is shown.
If what you want to do is trace the entire script as was done above (and not stop in the debugger when the script is over),
you can get the same effect by using the -X or --trace option on the bashdb command:
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the BASH debugger General Public License (GPL). The GPL gives you the freedom to copy or adapt a licensed program--but every person getting a copy also gets with it the freedom to modify that copy (which means that they must get access to the source code), and the freedom to distribute further copies. Typical software companies use copyrights to limit your freedoms; the Free Software Foundation uses the GPL to preserve these freedoms.
Fundamentally, the General Public License is a license which says that you have these freedoms and that you cannot take these freedoms away from anyone else.
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The biggest deficiency in the free software community today is not in the software--it is the lack of good free documentation that we can include with the free software. Many of our most important programs do not come with free reference manuals and free introductory texts. Documentation is an essential part of any software package; when an important free software package does not come with a free manual and a free tutorial, that is a major gap. We have many such gaps today.
Consider Perl, for instance. The tutorial manuals that people normally use are non-free. How did this come about? Because the authors of those manuals published them with restrictive terms--no copying, no modification, source files not available--which exclude them from the free software world.
That wasn't the first time this sort of thing happened, and it was far from the last. Many times we have heard a GNU user eagerly describe a manual that he is writing, his intended contribution to the community, only to learn that he had ruined everything by signing a publication contract to make it non-free.
Free documentation, like free software, is a matter of freedom, not price. The problem with the non-free manual is not that publishers charge a price for printed copies--that in itself is fine. (The Free Software Foundation sells printed copies of manuals, too.) The problem is the restrictions on the use of the manual. Free manuals are available in source code form, and give you permission to copy and modify. Non-free manuals do not allow this.
The criteria of freedom for a free manual are roughly the same as for free software. Redistribution (including the normal kinds of commercial redistribution) must be permitted, so that the manual can accompany every copy of the program, both on-line and on paper.
Permission for modification of the technical content is crucial too. When people modify the software, adding or changing features, if they are conscientious they will change the manual too--so they can provide accurate and clear documentation for the modified program. A manual that leaves you no choice but to write a new manual to document a changed version of the program is not really available to our community.
Some kinds of limits on the way modification is handled are acceptable. For example, requirements to preserve the original author's copyright notice, the distribution terms, or the list of authors, are ok. It is also no problem to require modified versions to include notice that they were modified. Even entire sections that may not be deleted or changed are acceptable, as long as they deal with nontechnical topics (like this one). These kinds of restrictions are acceptable because they don't obstruct the community's normal use of the manual.
However, it must be possible to modify all the technical content of the manual, and then distribute the result in all the usual media, through all the usual channels. Otherwise, the restrictions obstruct the use of the manual, it is not free, and we need another manual to replace it.
Please spread the word about this issue. Our community continues to lose manuals to proprietary publishing. If we spread the word that free software needs free reference manuals and free tutorials, perhaps the next person who wants to contribute by writing documentation will realize, before it is too late, that only free manuals contribute to the free software community.
If you are writing documentation, please insist on publishing it under the GNU Free Documentation License or another free documentation license. Remember that this decision requires your approval--you don't have to let the publisher decide. Some commercial publishers will use a free license if you insist, but they will not propose the option; it is up to you to raise the issue and say firmly that this is what you want. If the publisher you are dealing with refuses, please try other publishers. If you're not sure whether a proposed license is free, write to [email protected].
You can encourage commercial publishers to sell more free, copylefted manuals and tutorials by buying them, and particularly by buying copies from the publishers that paid for their writing or for major improvements. Meanwhile, try to avoid buying non-free documentation at all. Check the distribution terms of a manual before you buy it, and insist that whoever seeks your business must respect your freedom. Check the history of the book, and try to reward the publishers that have paid or pay the authors to work on it.
The Free Software Foundation maintains a list of free documentation published by other publishers, at http://www.fsf.org/doc/other-free-books.html.
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This chapter discusses how to start the BASH debugger, and how to get out of it. The essentials are:
source ../bashdb-trace and _Dbg_set_trace.
There are also two front-ends available as well. One can also enter the debugger inside emacs via the command M-x bashdb
after loading Emacs' Grand Unified Debugger, gud. See
Using the BASH debugger from GNU Emacs.
And there is support in a DDD for bash.
| 2.1 Starting the BASH debugger | How to enter the BASH debugger | |
| 2.2 Quitting the BASH debugger | How to leave the BASH debugger | |
| 2.3 Calling the BASH debugger from inside your program | Calling the debugger from inside your program |
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Note: it is important to use a debugger-enabled bash. You will get an error message if the debugger is run under a version of BASH that does not have debugging support.
As mentioned above, one can enter the BASH debugger DDD. However you don't have to use either of these. And these still need a way on their own to get things started.
There are in fact two other ways to start the BASH debugger. The first way is to pass the `--debugger'
option to bash with the name of your script the scripts arguments following that, or with a command string (-c).
bash --debugger script script-arguments... bash --debugger -c command-string... |
This calls a debugger initialization script. It works much like a BASH login profile which may set variables and define functions. But this shell profile is customized for debugging and as such arranges for itself to get called before each statement is executed. Although there are some problems at present in I/O redirection that the method described next doesn't have, it is expected that over time more features will be enabled in bash when the `--debugger' option is in effect. By default, both debugging in Emacs via GUD (Using the BASH debugger under Emacs) and debugging via DDD work via this method.
The form `bash --debugger -c ...' can be used to get into the debugger without having to give a script name to debug.
Sometimes you may want to do this just to see how the debugger works: try some debugger commands or maybe get online help. If you run
ddd --bash without giving a script name, it in fact uses this form.
In order for the `--debugger' option to work however, you must have the debugger scripts installed in a place where
the BASH debugger find them. For this reason, in developing the BASH debugger, I use a second
method more often; it doesn't require the bash debugger to be installed. This method uses another script called bashdb
which after taking its own options takes the name of the script to debugged and the arguments to pass to that script. Using this method,
one would start the debugger like this:
bash path-to-bashdb/bashdb bashdb-options script script-arguments... |
As with the first method, bash should be a debugger-enabled bash. If bashdb has the path to bash in it
at the top (e.g. via #!), and bashdb can be found in your program-search path, then this might be equivalent
to the above:
bashdb bashdb-options script script-arguments... |
There are two or three disadvantages however of running a debugger this way. First $0 will have the value bashdb
rather than the script you are trying to run. For some scripts this may change the behavior of the debugged script. Second a traceback
will contain additional lines showing the "source"-ing of the debugged script from bashdb. And third, although this way
works better than the first method, over time this way may come into disuse.
An option that you'll probably need to use if bashdb isn't installed but run out of the source code directory is `-L' which specifies the directory that contains the debugger script files.
You can further control how bashdb starts up by using command-line options. bashdb itself can remind you of the options available.
Type
bashdb -h |
to display all available options and briefly describe their use.
When the bash debugger is invoked either by the bashdb front-end script or bash --debugging, the first
argument that does not have an associated option flag for bashdb or bash (as the case may be) is used as the
name a the script file to be debugged, and any following options get passed the debugged script.
Options for the bashdb front-end are shown in the following list.
2.1.1 Command-line options
for bashdb script |
Options you can pass in starting bashdb |
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bashdb script You can run the BASH debugger mode or quiet mode. If getopts support is available the script also
allows long-form command options.
-h | --help This option causes the BASH debugger to print some basic help and exit.
-V This option causes the BASH debugger no-warranty blurb, and exit.
-c | --command cmd Run the string instead of running a script
-B | --basename This option causes the BASH debugger no-warranty blurb, and exit.
-n | --nx | --no-init Do not execute commands found in any initialization files. Normally, BASH executes the commands in these files after all the command options and arguments have been processed. See section Command files.
-q | --quiet "Quiet". Do not print the introductory and copyright messages. These messages are also suppressed in batch mode.
-t | --terminal | --tty tty "Terminal output". Set the file or terminal that you want debugger command output to go to. Note that the debugger output is independent of the debugged script output.
-L | --library directory Set directory where debugger files reside to directory. The default location is ../lib/bashdb relative
to the place that the bashdb script is located. For example if bashdb is located in /usr/local/bin/bashdb, the default
library location will be /usr/local/lib/bashdb which may or may not exist. If it doesn't you'll get an error when you
run bashdb. Only if the default location is incorrect, should you need to use the -L option.
-T | --tempdir directory Set directory to use for writing temporary files.
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An interrupt (often C-c) does not exit from the BASH debugger, but rather terminates the action of
any the BASH debugger progress and returns to the BASH debugger command level. Inside a debugger
command interpreter, use quit command (see section
Quitting the BASH debugger).
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Running a program from the debugger adds a bit of overhead and slows down your program quite a bit, and addressing this better would
mean some serious changes to BASH internals. If you have a configure script generated by autoconf, and
you want to stop in the middle of the script, it can take quite a while.
Furthermore, by necessity, debuggers change the operation of the program they are debugging. And this can lead to unexpected and unwanted differences. It has happened so often that the term "Heisenbugs" (see http://en.wikipedia.org/wiki/Heisenbug) was coined to describe the situation where the addition of the use of a debugger (among other possibilities) changes behavior of the program so that the bug doesn't manifest itself anymore.
Another way to get into the debugger which adds no overhead or slowdown until you reach the point at which you want to start debugging. However here you must change the script and make an explicit call to the debugger. Because the debugger isn't involved before the first call, there is no overhead and the script will run at the same speed as if there were no debugger.
There are two parts to calling the debugger from inside the script, "sourcing" in the debugger code and then making the call calling
the debugger to issue a "step" command. The name of file in source command is bashdb-trace and it is located
in the directory where the other bash debugger files live. For example on GNU/Linux if it is in directory /usr/local/share/bashdb,
you would first add to a BASH script the line:
source /usr/local/share/bashdb/bashdb-trace |
Although I said that running under the debugger adds overhead which slows down you program, the above command in of itself will
not cause any slowdown. If possible, it's best to put this somewhere in the main-line code rather than in a function or in
a subshell. If it is put in a function of subshell and you step outside of that, some of the global variables set up in bashdb-trace
may be lost. One the other hand if you know your debugging will be confined to just the scope of the source command there
is no problem.
The second thing that needs to be done is put add statements to start stepping code, and this line looks like this:
_Dbg_set_trace ; : ; : |
(For reasons that are a mystery to me, the stepping seems to kick in only two statements after the call.)
Putting these two components together, here's an example:
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You will be stopped before y=3 in the debugger.
You can also supply options to _Dbg_bash_trace just as you would to the debugger itself. All of the options listed in
Command-line options for bashdb script can
be used with the exception of -c (run a command) and of course you don't supply the name of a BASH script.
For example to suppress the banner you could use _Dbg_bash_trace -q in the above example.
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| 3.1 Starting your script | ||
| 3.2 Command files | ||
| 3.3 Your script's arguments | ||
| 3.4 Your script's input and output | ||
| 3.5 Script/Debugger Interaction | Keeping out of each other's harm |
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restart [options to debugged script] run R Use the restart command to restart your script under the BASH debugger. Without any arguments,
the script name and parameters from the last invocation are used. The BASH debugger tries to maintain the settings,
watchpoints, breakpoints, actions and so on. Internally it uses line numbers and filenames to record he position of interesting places
in your porgram; so if your program changes some or all of these numbers may be off. Environment variable BASHDB_RESTART_FILE
is and a temporary file are used to signal a restart, so you shouldn't uset BASHDB_RESTART_FILE (or any environment
variable starting with BASHDB_.
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A command file for the BASH debugger commands. Comments (lines starting with #) may also be included. An empty line in a command file does nothing; it does not mean to repeat the last command, as it would from the terminal.
When you start the BASH debugger, it automatically executes commands from its init files, normally called `.bashdbinit'(1). During startup, the BASH debugger
The init file in your home directory can set options (such as `set complaints') that affect subsequent processing of command line options and operands. Init files are not executed if you use the `-x' option (see section bashdb script options).
On some configurations of the BASH debugger, the init file is known by a different name (these are typically environments where a specialized form of the BASH debugger different name for the specialized version's init file). These are the environments with special init file names:
You can also request the execution of a command file with the source command:
source filename Execute the command file filename.
The lines in a command file are executed sequentially. They are not printed as they are executed. If there is an error, execution proceeds to the next command in the file.
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The arguments to your script can be specified by the arguments of the restart command. They are passed to a shell, which
expands wildcard characters and performs redirection of I/O, and thence to your script.
restart with no arguments uses the same arguments used by the previous restart, or those set by the
set args command..
set args Specify the arguments to be used the next time your program is run. If set args has no arguments, restart
executes your program with no arguments. Once you have run your program with arguments, using set args before the next
restart is the only way to run it again without arguments.
show args Show the arguments to give your program when it is started.
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By default, the script you run under the BASH debugger does input and output to the same terminal that BASH uses. Before running the script to be debugged, the debugger records the tty that was in effect. All of its output is then written to that. However you can change this when using the `bashdb' script using the `-t' option.
info terminal Displays information recorded by the BASH debugger program is using.
Another way to specify where your script should do input and output is with the tty command. This command accepts a
file name as argument, and causes this file to be the default for future restart commands. It also resets the controlling
terminal for the child process, for future restart commands. For example,
tty /dev/ttyb |
directs that processes started with subsequent restart commands default to do input and output on the terminal `/dev/ttyb'
and have that as their controlling terminal.
An explicit redirection in restart overrides the tty command's effect on the input/output device, but not
its effect on the controlling terminal.
When you use the tty command or redirect input in the restart command, only the input for your script
is affected. The input for the BASH debugger
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The BASH debugger and your program live in the same variable space so to speak. BASH does not have a notion of module scoping or lexical hiding (yet) and this then imposes some additional care and awareness.
Most of the variables and functions used inside the BASH debugger _Dbg_, so please don't use variables
or functions with these names in your program.
Note: there are some other variables that begin with just an underscore (_); over time these will be phased out.
But until then, avoid those or consult what is used by the debugger. Run `bashdb --debugger -c 'declare -p'' to list all
the variables in use including those used by the debugger.
A number of the BASH debugger use; these start with BASHDB_. For example: BASHDB_INPUT,
BASHDB_LEVEL and, BASHDB_QUIT_ON_QUIT (see section
Debug), BASHDB_RESTART_FILE (see section
Starting), to name a few. Finally, there are some
BASH environment dynamic variables and these start with BASH_. For example BASH_SUBSHELL
(see section Debug), BASH_COMMAND (see section
Command Display), BASH_LINENO, and
BASH_SOURCE to name a few.
In order to do its work The BASH debugger sets up a DEBUG trap. Consequently a script shouldn't reset
this or the debugger will lose control. The BASH debugger also sets up an EXIT handler so that it can
gain control after the script finishes. Another signal intercepted is the an interrupt or INT signal. For more information
about signal handling, see section Signals
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You can abbreviate the long name of the BASH debugger few letters of the command name, if that abbreviation is
unambiguous; and you can repeat the next o rstep commands by typing just RET. Some commands which
require a parameter, such as print remember the argument that was given to them.
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A BASH debugger command is a single line of input. There is no limit on how long it can be. It starts with a command
name, which is followed by arguments whose meaning depends on the command name. For example, the command step accepts an
argument which is the number of times to step, as in `step 5'. You can also use the step command with no arguments.
Some commands do not allow any arguments.
A blank line as input to the BASH debugger repeat the previous next or step command.
Any text from a # to the end of the line is a comment; it does nothing. This is useful mainly in command files (see section Command files).
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Once inside the BASH debugger, you can always ask it for information on its commands, using the command
help.
help h You can use help (abbreviated h) with no arguments to display a short list of named classes of commands:
bashdb<0> help
bashdb commands:
List/search source lines: Control script execution:
------------------------- -------------------------
l [start|.] [cnt] List cnt lines T [n] Stack trace
from line start s [n] Single step [n times]
l sub List source code fn n [n] Next, steps over subs
- or . List previous/current line <CR>/<Enter> Repeat last n or s
w [line] List around line c [linespec] Continue [to linespec]
f filename View source in file L List all breakpoints
/pat/ Search forward for pat b linespec Set breakpoint
?pat? Search backward for pat del [n].. or D Delete a/all breaks
by entry number
Debugger controls: skip skip execution of cmd
------------------------- cl linespec Delete breakpoints by
H [num] Show last num commands line spec
q [exp] or ^D Quit returning exp R [args] Attempt a restart
info [cmd] Get info on cmd. u [n] Go up stack by n or 1.
!n or hi n Run debugger history n do [n] Go down stack by n or 1.
h or ? [cmd] Get help on command W [var] Add watchpoint. If no
info [cmd] Get info on cmd no expr, delete all
show [cmd] Show settings We [expr] Add Watchpoint arith
expr
so file read in dbg commands t Toggle trace
en/di n enable/disable brkpt,
set x y set a debugger variable watchpoint, or display
e bash-cmd evaluate a bash command tb linespec Add one-time break
disp expr add a display expr a linespec cmd eval "cmd" at linespec
M Show module versions A delete all actions
x expr evaluate expression ret jump out of fn or source
(via declare, let, eval) finish execute until return
deb debug into another cond n exp set breakpoint condition
shell script
!! cmd [args] execute shell command "cmd" with "args"
file filename Set script filename to read for current source.
Data Examination: also see e, t, x
-------------------------
p variable Print variable
V [[!]pat] List variable(s) matching or not (!) matching pattern pat
S [[!]pat] List subroutine names [not] matching pattern pat
Readline command line editing (emacs/vi mode) is available.
For more help, type h <cmd> or consult online-documentation.
|
help command With a command name as help argument, the BASH debugger displays short information on how to use
that command.
bashdb<0> help list
l linespec List window lines starting at linespec.
l min incr List incr lines starting at 'min' linespec.
l List next window of lines.
l . Same as above.
Long command name: list.
|
In addition to help, you can use the debugger command info to inquire about the state of your script,
or the state of the BASH debugger point to all the sub-commands. See section
Command Index.
info This command (abbreviated i) is for describing the state of your program. For example, you can list the arguments
given to your script with info args, or list the breakpoints you have set with info breakpoints. You can
get a complete list of the info sub-commands with help info.
bashdb<0> help info List of info subcommands: info args -- Argument variables (e.g. $1, $2, ...) of the current stack frame. info breakpoints -- Status of user-settable breakpoints info display -- Show all display expressions info files -- Source files in the program info functions -- All function names info line -- list current line number and and file name info program -- Execution status of the program. info signals -- What debugger does when program gets various signals info source -- Information about the current source file info stack -- Backtrace of the stack info terminal -- Print terminal device info variables -- All global and static variable names info warranty -- Various kinds of warranty you do not have bashdb<1> info source Current script file is parm.sh Contains 34 lines. |
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quit [expression] quit [expression [subshell-levels]] q To exit the BASH debugger, use the quit command (abbreviated q), or type an end-of-file
character (usually C-d). If you do not supply expression, the BASH debugger normally or
with exit code 0. Otherwise it will terminate using the result of expression as the exit code.
A simple quit tries to terminate all nested subshells that may be in effect. If you are nested a subshell, this is
normally indicated in a debugger prompt by the number of parentheses that the history number is inside -- no parenthesis means there
is no subshell in effect. The dynamic variable BASH_SUBSHELL also contains the number of subshells in effect.
If you want only to terminate some number of subshells but not all of them, you can give a count of the number of subshells to
leave after the return-code expression. To leave just one level of subshell return does almost the same thing. (See
see section Returning) There is a subtle difference
between the two though: return will leave you at the beginning of the next statement while quit may leave
you at the place the subshell was invoked which may be in the middle of another command such as an assingment statement or condition
test.
If the environment variable BASHDB_QUIT_ON_QUIT is set, when the program terminates, the debugger will also terminate
too. This may be useful if you are debugging a script which calls another script and you want this inner script just to return to
the outer script.
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One important use of a debugger is to stop your program before it terminates so that, if your script might run into trouble, you can investigate and find out why. However should your script accidently continue to termination, the BASH debugger debugger without your explicit instruction. That way, you can restart the program using the same command arguments.
Inside the BASH debugger, your script may stop for any of several reasons, such as a signal, a breakpoint, or
reaching a new line after a debugger command such as step. You may then examine and change variables, set new breakpoints
or remove old ones, and then continue execution.
| 4.4.1 Breakpoints, watchpoints (`break', `tbreak', `watch', `watche'...) | Breakpoints, watchpoints (break, tbreak, watch, watche, clear) | |
| 4.4.2 Resuming Execution (`step', `next', `finish', `skip', `continue', `debug', `return') | Resuming execution (continue, step, next, skip, debug) | |
| 4.4.3 Signals |
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A breakpoint makes your script stop whenever a certain point in the program is reached. For each breakpoint, you can add conditions to control in finer detail whether your script stops.
You can set breakpoints with the break command and its variants (see section
Setting breakpoints), to specify the place where your
script should stop by line number. or function name in the debugged script.
A watchpoint is a special breakpoint that stops your script when the value of an expression changes. There is a different command to set watchpoints (see section Setting watchpoints).
But aside from that, you can manage a watchpoint like any other breakpoint: you delete enable, and disable both breakpoints and watchpoints using the same commands.
You can arrange to have values from your program displayed automatically whenever BASH stops at a breakpoint. See section Automatic display.
The BASH debugger assigns a number to each breakpoint and watchpoint when you create it; these numbers are successive integers starting with one. In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change. Each breakpoint may be enabled or disabled; if disabled, it has no effect on your script until you enable it again.
Watchpoint numbers however are distinguished from breakpoint numbers by virtue of their being suffixed with the either an upper- or lower-case `W'. For example, to enable breakpoint entry 0 along with watchpoint entry 1 you would write `enable 1 2w', the "2w" refers to the watchpoint; "2W" would work just as well.
| 4.4.1.1 Setting breakpoints (`break' `tbreak') | Setting breakpoints (break, tbreak) | |
| 4.4.1.2 Setting watchpoints (`watch', `watche') | Setting watchpoints (watch, watche) | |
| 4.4.1.3 Breakpoint command lists (`commands') | Breakpoint command lists (command) | |
| 4.4.1.4 Deleting breakpoints (`clear', `delete') | Deleting breakpoints (delete, clear) | |
| 4.4.1.5 Disabling breakpoints (`disable', `enable') | Disabling breakpoints (disable, enable) | |
| 4.4.1.6 Break conditions (`condition') | Break conditions (condition) |
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Breakpoints are set with the break command (abbreviated b).
break function Set a breakpoint at entry to function function.
break linenum Set a breakpoint at line linenum in the current source file. The current source file is the last file whose source text was printed. The breakpoint will stop your script just before it executes any of the code on that line.
break filename:linenum Set a breakpoint at line linenum in source file filename; filename has to be one of the files previously read in and has to be specified exactly as the name used when read in. For a list of read-in files, use the `info files' command.
break � if cond Set a breakpoint with condition cond; evaluate the expression cond each time the breakpoint is reached,
and stop only if the value is nonzero--that is, if cond evaluates as true. The expression is evaluated via the let
builtin funtion. `�' stands for one of the possible arguments described above (or no argument) specifying where to break.
The word "if" is often optional and is necessary only `�' is omitted. See section
Break conditions, for more information on breakpoint
conditions.
Examples:
bashdb<0> break fn1 Breakpoint 1 set in file parm.sh, line 3. bashdb<1> break 28 Breakpoint 2 set in file parm.sh, line 28. bashdb<2> break parm.sh:29 Breakpoint 3 set in file parm.sh, line 29. bashdb<3> break 28 if x==5 Breakpoint 4 set in file parm.sh, line 28. |
tbreak args Set a breakpoint enabled only for one stop. args are the same as for the break command, and the breakpoint
is set in the same way, but the breakpoint is automatically deleted after the first time your program stops there. See section
Disabling breakpoints.
info breakpoints [n] info break [n] info watchpoints [n] Print a table of all breakpoints, watchpoints set and not deleted, with the following columns for each breakpoint:
Enabled breakpoints are marked with `1'. `0' marks breakpoints that are disabled (not enabled).
The number of times that breakpoint or watchpoint has been hit.
The arithmetic expression
The filename and line number inside that file where of breakpoint in the script. The file and line are separated with a colon.
If a breakpoint is conditional, info break shows the condition on the line following the affected breakpoint; breakpoint
commands, if any, are listed after that.
info break displays a count of the number of times the breakpoint has been hit.
info break with a breakpoint number n as argument lists only that breakpoint.
Examples:
bashdb<4> info break Breakpoints at following places: Num Type Disp Enb What 1 breakpoint keep y parm.sh:3 2 breakpoint keep y parm.sh:28 3 breakpoint keep y parm.sh:29 4 breakpoint keep y parm.sh:28 No watch expressions have been set. bashdb<5> info break 4 Num Type Disp Enb What 4 breakpoint keep y parm.sh:28 No watch expressions have been set. |
the BASH debugger your script. There is nothing silly or meaningless about this. When the breakpoints are conditional, this is even useful (see section Break conditions).
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You can use a watchpoint to stop execution whenever the value of an expression changes, without having to predict a particular place
where this may happen. As with the print (see section
Examining Data), the idiosyncracies of a BASH
or any POSIX shell derivative suggest using two commands. The watch command is just for a single variables; the watche
command uses the builtin "let" command to evaluate an expression. If the variable you are tracking can take a string value, issuing
something like `watch foo' will not have the desired effect--any string assignment to foo will have a value
0 when it is assigned via "let."
watch var Set a watchpoint for a variable. the BASH debugger value of var changes. In this command do not add a leading dollar symbol to var.
watche expr Set a watchpoint for an expression via the builtin "let" command. the BASH debugger and its value changes.
Not that this may not work for tracking arbitrary string value changes. For that use watch described earlier.
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commands [bnum] � command-list � end Specify a list of commands for breakpoint number bnum. The commands themselves appear on the following lines. Type
a line containing just end to terminate the commands.
To remove all commands from a breakpoint, type commands and follow it immediately with end; that is,
give no commands.
With no bnum argument, commands refers to the last breakpoint, watchpoint, or catchpoint set (not to the
breakpoint most recently encountered).
Pressing RET as a means of repeating the last debugger command is disabled within a command-list.
You can use breakpoint commands to start your program up again. Simply use the continue command, or step,
or any other command that resumes execution.
Any other commands in the command list, after a command that resumes execution, are ignored. This is because any time you resume
execution (even with a simple next or step), you may encounter another breakpoint--which could have its own
command list, leading to ambiguities about which list to execute.
If the first command you specify in a command list is silent, the usual message about stopping at a breakpoint is not
printed. This may be desirable for breakpoints that are to print a specific message and then continue. If none of the remaining commands
print anything, you see no sign that the breakpoint was reached. silent is meaningful only at the beginning of a breakpoint
command list.
The commands echo, output, and printf allow you to print precisely controlled output, and
are often useful in silent breakpoints.
For example, here is how you could use breakpoint commands to print the value of x at entry to foo whenever
x is positive.
break foo if x>0 commands silent printf "x is %d\n",x cont end |
One application for breakpoint commands is to compensate for one bug so you can test for another. Put a breakpoint just after the
erroneous line of code, give it a condition to detect the case in which something erroneous has been done, and give it commands to assign
correct values to any variables that need them. End with the continue command so that your program does not stop, and start
with the silent command so that no output is produced. Here is an example:
break 403 commands silent set x = y + 4 cont end |
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It may desirable to eliminate a breakpoint or watchpoint once it has done its job and you no longer want your script to stop there. This is called deleting the breakpoint. A breakpoint that has been deleted no longer exists; it is forgotten.
With the clear command you can delete breakpoints according to where they are in your script. With the delete
command you can delete individual breakpoints, or watchpoints by specifying their breakpoint numbers. Note: as described below under
the "clear" command, "d" is an alias for "clear", not "delete".
It is not necessary to delete a breakpoint to proceed past it. the BASH debugger automatically ignores breakpoints on the first instruction to be executed when you continue execution.
clear Delete any breakpoints at the next instruction to be executed in the selected stack frame (see section Selecting a frame). When the innermost frame is selected, this is a good way to delete a breakpoint where your script just stopped.
It may seem odd that we have an alias "d" for "clear." It so happens that Perl's debugger use "d" for its delete command and the delete concept in Perl's debugger corresponds to "clear" in GDB. (Perl doesn't have a notion of breakpoint entry numbers). So in order to be compatible with both debugger interfaces, "d" is used as an alias for "clear." Clear?
clear function clear filename:function Delete any breakpoints set at entry to the function function.
clear linenum d linenum Delete any breakpoints set at or within the code of the specified line.
delete [breakpoints] Delete the breakpoints, watchpoints specified as arguments.
If no argument is specified, delete all breakpoints (the BASH debugger confirmation, unless you have
set confirm off). You can abbreviate this command as de.
Note that for compatibility with Perl's debugger, d means something else: clear.
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Rather than deleting a breakpoint or watchpoint, you might prefer to disable it. This makes the breakpoint inoperative as if it had been deleted, but remembers the information on the breakpoint so that you can enable it again later.
You disable and enable breakpoints, watchpoints, and catchpoints with the enable and disable commands,
optionally specifying one or more breakpoint numbers as arguments. Use info break or info watch to print a
list of breakpoints, watchpoints, and catchpoints if you do not know which numbers to use.
A breakpoint, watchpoint, or catchpoint can have any of four different states of enablement:
break command starts out in this state.
tbreak command starts out in this state. You can use the following commands to enable or disable breakpoints, watchpoints, and catchpoints:
disable [breakpoints] Disable the specified breakpoints--or all breakpoints, if none are listed. A disabled breakpoint has no effect but is not forgotten.
All options such as ignore-counts, conditions and commands are remembered in case the breakpoint is enabled again later. You may
abbreviate disable as dis.
enable [breakpoints] Enable the specified breakpoints (or all defined breakpoints). They become effective once again in stopping your program.
Except for a breakpoint set with tbreak (see section
Setting breakpoints), breakpoints that you set are initially
enabled; subsequently, they become disabled or enabled only when you use one of the commands above. (The command until
can set and delete a breakpoint of its own, but it does not change the state of your other breakpoints; see
Resuming Execution.)
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The simplest sort of breakpoint breaks every time your script reaches a specified place. You can also specify a condition for a breakpoint. A condition is just a BASH expression.
Break conditions can be specified when a breakpoint is set, by using `if' in the arguments to the break
command. See section Setting breakpoints. A breakpoint
with a condition evaluates the expression each time your script reaches it, and your script stops only if the condition is true.
There is also a notion of a "one-time" breakpoint which gets deleted as soon as it is hit, so that that breakpoint is executed once only.
Conditions are also accepted for watchpoints; you may not need them, since a watchpoint is inspecting the value of an expression anyhow--but it might be simpler, say, to just set a watchpoint on a variable name, and specify a condition that tests whether the new value is an interesting one.
Break conditions can be specified when a breakpoint is set, by using `if' in the arguments to the break
command. See section Setting breakpoints. They can also
be changed at any time with the condition command.
condition bnum expression Specify expression as the break condition for breakpoint bnum. After you set a condition, breakpoint bnum stops your program only if the value of expression is true (nonzero).
condition bnum Remove the condition from breakpoint number bnum. It becomes an ordinary unconditional breakpoint.
BASH does not actually evaluate expression at the time the condition command (or a command
that sets a breakpoint with a condition, like break if �) is given, however.
Examples;
condition 1 x>5 # Stop on breakpoint 0 only if x>5 is true. condition 1 # Change that! Unconditinally stop on breakpoint 1. |
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Continuing means resuming program execution until your script completes normally. In contrast, stepping means executing just one more "step" of your script, where "step" may mean either one line of source code. Either when continuing or when stepping, your script may stop even sooner, due to a breakpoint or a signal.
| 4.4.2.1 Step (`step') | running the next statement (step) | |
| 4.4.2.2 Next (`next') | running the next statement skipping over functions (skip) | |
| 4.4.2.3 Finish (`finish') | running until the return of a function or "source" (finish) | |
| 4.4.2.4 Skip (`skip') | skipping the next statement (skip) | |
| 4.4.2.5 Continue (`continue') | continuing execution (continue) | |
| 4.4.2.6 Debug (`debug') | debugging into another program (debug) | |
| 4.4.2.7 Returning from a function, sourced file, or subshell (`return') | returning |
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step Continue running your script until control reaches a different source line, then stop it and return control to the BASH
debugger. This command is abbreviated s.
The step command only stops at the first instruction of a source line. This prevents the multiple stops that could
otherwise occur in switch statements, for loops, etc. step continues to stop if a function
that has debugging information is called within the line. In other words, step steps inside any functions called
within the line.
step [count] Continue running as in step, but do so count times. If a breakpoint is reached, or a signal not related
to stepping occurs before count steps, stepping stops right away.
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next [count] Continue to the next source line in the current (innermost) stack frame. This is similar to step, but function calls
that appear within the line of code are executed without stopping. Execution stops when control reaches a different line of code
at the original stack level that was executing when you gave the next command. This command is abbreviated n.
An argument count is a repeat count, as for step.
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finish Continue running until just after function returns. Currently, the line shown on a return is the function header, unless the
return builtin function is executed in which case it is the line number of the return function.
Contrast this with the return command (see section
Returning from a function) and the quit
(see section Quitting the BASH debugger).
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skip [count] Skip execution of the next source line. This may be useful if you have an action that "fixes" existing code in the script. The
debug command internally uses the skip command to skip over existing non-debugged invocation that was presumably
just run.
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continue [linespec] c [line-number] Resume program execution, at the address where your script last stopped; any breakpoints set at that address are bypassed. The optional argument linespec allows you to specify a linespec (a line number, function, or filename linenumber combination) to set. A one-time breakpoint is deleted when that breakpoint is reached. Should the program stop before that breakpoint is reached, for example, perhaps another breakpoint or watchpoint is reached first, in a listing of the breakpoints you will see this entry with the condition 9999 which indicates a one-time breakpoint.
To resume execution at a different place, you can use return (see section
Returning from a function) to go back to the calling function
or sourced script. If you are nested inside a subshell, quit with a value for the number of subshells to exit also functions
like a return.
A typical technique for using stepping is to set a breakpoint (see section Breakpoints; watchpoints) at the beginning of the function or the section of your script where a problem is believed to lie, run your script until it stops at that breakpoint, and then step through the suspect area, examining the variables that are interesting, until you see the problem happen.
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debug [script-name] Debug into script-name. If no name is given the current source line is used. In either case the options are prepended to cause the debugger to run.
The nesting level of the debugger is saved inside environment variable BASHDB_LEVEL. The debugger prompt indicates
the level of nesting by enclosing the history in that many nestings of <> symbols.
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return return You can cancel execution of a function call or a subshell with the return command.
The return command does not resume execution; it leaves the program stopped in the state that would exist if the function
had just returned. See also the quit command (Quitting
the BASH debugger). In some situations return is similar to quit: in particular when the script is
not currenlty inside in a function and the number of subshells in effect is 0, or when a subshell count of 1 is given on the
quit command.
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A signal is an asynchronous event that can happen in a program. The operating system defines the possible kinds of signals, and gives
each kind a name and a number. For example, in Unix SIGINT is the signal a program gets when you type an interrupt character
(often C-c); SIGALRM occurs when the alarm clock timer goes off (which happens only if your program has requested
an alarm).
Some signal handlers are installed and changed for the BASH debugger's normal use: SIGDEBUG and
SIGEXIT. SIGDEBUG is used by the debugger to potentially stop your program before execution of each statement
occurs, and SIGEXIT is used to catch your program just before it is set to leave so you have the option of restarting the
program with the same options (and not leave the debugger) or let the program quit.
Signal handlers that the debugged script might have installed are saved and called before the corresponding debugger handler. Thus,
the debugged program should work roughly in the same fashion as when it is not debugged. However there are some call-stack variables
which inevitably will differ. To try to hedge this a little so the behaviour is the same, the BASH debugger will
modify arguments to the traps if it finds one of the call-stack that change as a result of the debugger being in place. In particluar
$LINENO will get replaced with ${BASH_LINENO[0]}; also ${BASH_LINENO[0]} and ${BASH_SOURCE[0]}
get replaced with ${BASH_LINENO[1]} and ${BASH_SOURCE[1]} respectively.
The debugger also installs an interrupt handler SIGINT so that errant programs can be interrupted and you can find out
where the program was when you interrupted it.
Some signals, including SIGALRM, are a normal part of the functioning of your program. Others, such as SIGSEGV,
indicate errors; these signals are fatal (they kill your program immediately) if the program has not specified in advance some
other way to handle the signal. SIGINT does not indicate an error in your program, but it is normally fatal so it can carry
out the purpose of the interrupt: to kill the program.
BASH has the ability to detect any occurrence of a signal in your program. You can tell BASH in advance what to do for each kind of signal.
Normally, BASH is set up to let the non-erroneous signals like SIGALRM be silently passed to your
program (so as not to interfere with their role in the program's functioning) but to stop your program immediately whenever an error
signal happens. You can change these settings with the handle command.
info signals info handle Print a table of all the kinds of signals and how BASH has been told to handle each one. You can use this to see the signal numbers of all the defined types of signals.
info handle is an alias for info signals.
handle signal keywords� Change the way BASH handles signal signal. signal can be the number of a signal or its name (with or without the `SIG' at the beginning); a list of signal numbers of the form `low-high'; or the word `all', meaning all the known signals. The keywords say what change to make.
The keywords allowed by the handle command can be abbreviated. Their full names are:
stop BASH should stop your program when this signal happens. This implies the print keyword as well.
nostop BASH should not stop your program when this signal happens. It may still print a message telling you that the signal has come in.
print BASH should print a message when this signal happens.
noprint BASH should not mention the occurrence of the signal at all.
stack BASH should print a stack trace when this signal happens.
nostack BASH should not print a stack trace when this signal occurs.
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| 4.5.1 Showing information about the program being debugged (`info') | Showing information about the program being debugged | |
| 4.5.2 Show information about the debugger (`show') | Show information about the debugger |
In addition to help, you can use the BASH commands info and show to inquire
about the state of your program, or the state of BASH itself. Each command supports many topics of inquiry; here
we introduce each of them in the appropriate context. The listings under info and under show in the Index
point to all the sub-commands. See section Command Index.
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This info command (abbreviated i) is for describing the state of your program. For example, you can list
the current $1, $2 parameters with info args, or list the breakpoints you have set with
info breakpoints or info watchpoints. You can get a complete list of the info sub-commands with
help info.
info args Argument variables (e.g. $1, $2, ...) of the current stack frame.
info breakpoints info display info files info functions info line info program info signals info source info stack info terminal info variables All global and static variable names
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In contrast to info, show is for describing the state of BASH itself. You can change
most of the things you can show, by using the related command set;
The distinction between info and show however is a bit fuzzy and is kept here to try to follow the GDB
interface. For example, to list the arguments given to your script use show args; info args does something
different.
Here are three miscellaneous show subcommands, all of which are exceptional in lacking corresponding set
commands:
show version Show what version of BASH is running. You should include this information in BASH bug-reports. If multiple versions of BASH are in use at your site, you may need to determine which version of BASH you are running; as BASH evolves, new commands are introduced, and old ones may wither away. Also, many system vendors ship variant versions of BASH, and there are variant versions of BASH in GNU/Linux distributions as well. The version number is the same as the one announced when you start BASH.
show copying Display information about permission for copying BASH.
show linetrace Show if line tracing is enabled. See also Show position information as statements are executed (`set linetrace').
show logging Show summary information of logging variables which can be set via set logging. See also
Logging output (`set logging', `set
logging file'...).
show logging file Show the current logging file.
show logging overwrite Show whether logging overwrites or appends to the log file.
show warranty Display the GNU "NO WARRANTY" statement, or a warranty, if your version of the BASH debugger
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When your script has stopped, one thing you'll probably want to know is where it stopped and some idea of how it got there.
Each time your script performs a function call (either as part of a command substitution or not), or `source's a file, information about this action is saved. The call stack then is this a history of the calls that got you to the point that you are currently stopped at.
One of the stack frames is selected by the BASH debugger the BASH debugger particular, whenever you ask the BASH debugger a line number or location the value is found in the selected frame. There are special the BASH debugger are interested in. See section Selecting a frame.
When your program stops, BASH automatically selects the currently executing frame and describes it briefly, similar
to the frame command.
| 4.6.1 Stack frames | ||
| 4.6.2 Backtraces (`where') | Backtraces (where) | |
| 4.6.3 Selecting a frame (`up', `down', `frame') | Selecting a frame (up, down, frame) | |
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The call stack is divided up into contiguous pieces called stack frames, or frames for short; each frame is the data associated with one call to one function. The frame contains the line number of the caller of the function, the source-file name that the line refers to a function name (which could be the built-in name "source")..
When your script is started, the stack has only one frame, that of the function main. This is called the initial
frame or the outermost frame. Each time a function is called, a new frame is made. Each time a function returns, the frame
for that function invocation is eliminated. If a function is recursive, there can be many frames for the same function. The frame for
the function in which execution is actually occurring is called the innermost frame. This is the most recently created of all
the stack frames that still exist.
the BASH debugger assigns numbers to all existing stack frames, starting with zero for the innermost frame, one for the frame that called it, and so on upward. These numbers do not really exist in your script; they are assigned by the BASH debugger to give you a way of designating stack frames in the BASH debugger commands.
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A backtrace is essentially the same as the call stack: a summary of how your script got where it is. It shows one line per frame, for many frames, starting with the place that you sare stopped at (frame zero), followed by its caller (frame one), and on up the stack.
backtrace bt where T Print a backtrace of the entire stack: one line per frame for all frames in the stack.
backtrace n bt n where n T n Similar, but print only the innermost n frames.
The names where and T are additional aliases for backtrace.
Each line in the backtrace shows the frame number and the function name, the source file name and line number, as well as the function name.
Here is an example of a backtrace taken a program in the regression-tests `parm.sh'.
% ../bashdb -n -L .. parm.sh
Bourne-Again Shell Debugger, release 3.1-0.06
Copyright 2002, 2003, 2004, 2006 Rocky Bernstein
This is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
(./parm.sh:21):
21: fn1 5
bashdb<0> continue fn3
One-time breakpoint 1 set in file ./parm.sh, line 17.
fn2: testing 1 2 3
(./parm.sh:17):
17: fn3() {
bashdb<1> where
->0 in file `./parm.sh' at line 14
##1 fn3() called from file `./parm.sh' at line 14
##2 fn2("testing 1", "2 3") called from file `parm.sh' at line 5
##3 fn1("0") called from file `parm.sh' at line 9
##4 fn1("1") called from file `parm.sh' at line 9
##5 fn1("2") called from file `parm.sh' at line 9
##6 fn1("3") called from file `parm.sh' at line 9
##7 fn1("4") called from file `parm.sh' at line 9
##8 fn1("5") called from file `parm.sh' at line 21
##9 source("parm.sh") called from file `bashdb' at line 143
##10 main("-n", "-L", "..", "parm.sh") called from file `bashdb' at line 0
|
The display for "frame" zero isn't a frame at all, although it has the same information minus a function name; it just indicates
that your script has stopped at the code for line 14 of ./parm.sh.
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Commands for listing source code in your script work on whichever stack frame is selected at the moment. Here are the commands for selecting a stack frame; all of them finish by printing a brief description of the stack frame just selected.
up n Move n frames up the stack. For positive numbers n, this advances toward the outermost frame, to higher frame numbers, to frames that have existed longer. n defaults to one.
down n Move n frames down the stack. For positive numbers n, this advances toward the innermost frame, to lower
frame numbers, to frames that were created more recently. n defaults to one. You may abbreviate down as
do.
All of these commands end by printing two lines of output describing the frame. The first line shows the frame number, the function name, the arguments, and the source file and line number of execution in that frame. The second line shows the text of that source line.
For example:
|
After such a printout, the list command with no arguments prints ten lines centered on the point of execution in the
frame. See section Printing source lines.
frame args The frame command allows you to move from one stack frame to another, and to print the stack frame you select.
args is the the stack frame number. Without an argument, frame prints the current stack frame.
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the BASH debugger can print parts of your script's source. When your script stops, the BASH debugger spontaneously prints the line where it stopped. Likewise, when you select a stack frame (see section Selecting a frame), the BASH debugger prints the line where execution in that frame has stopped. You can print other portions of source files by explicit command.
If you use the BASH debugger through its GNU Emacs interface, you may prefer to use Emacs facilities to view source; see Using the BASH debugger under GNU Emacs.
To print lines from a source file, use the list command (abbreviated l). By default, ten lines are printed.
There are several ways to specify what part of the file you want to print.
Here are the forms of the list command most commonly used:
list linenum l linenum Print lines centered around line number linenum in the current source file.
list function l function Print the text of function.
list l Print more lines. If the last lines printed were printed with a list command, this prints lines following the last
lines printed; however, if the last line printed was a solitary line printed as part of displaying a stack frame (see section
Examining the Stack), this prints lines centered around
that line.
list - l - Print lines just before the lines last printed.
By default, the BASH debugger prints ten source lines with any of these forms of the list command.
You can change this using set listsize:
set listsize count Make the list command display count source lines (unless the list argument explicitly specifies
some other number).
show listsize Display the number of lines that list prints.
Repeating a list command with RET discards the argument, so it is equivalent to typing just list.
This is more useful than listing the same lines again. An exception is made for an argument of `-'; that argument is preserved
in repetition so that each repetition moves up in the source file.
In general, the list command expects you to supply a linespecs. Linespecs specify source lines; there are several
ways of writing them, but the effect is always to specify some source line.
Here is a complete description of the possible arguments for list:
list linespec Print lines centered around the line specified by linespec.
list first increment Print increment lines starting from first
list first Print lines starting with first.
list - Print lines just before the lines last printed.
list . Print lines after where the script is stopped.
list As described in the preceding table.
Here are the ways of specifying a single source line--all the kinds of linespec.
number Specifies line number of the current source file. When a list command has two linespecs, this refers to
the same source file as the first linespec.
filename:number Specifies line number in the source file filename.
function Specifies the line that function function is listed on.
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There are two commands for searching through the current source file for a BASH extended pattern-matching expression.
forward bash-pattern search bash-pattern The command `forward bash-pattern' checks each line, starting with the one following the current line,
for a match for bash-pattern which is an extended bash pattern-matching expression. It lists the line that is found. You
can use the synonym `search bash-pattern' or abbreviate the command name as fo or /pat/.
reverse bash-pattern The command `reverse bash-pattern' checks each line, starting with the one before the last line listed
and going backward, for a match for bash-pattern. It lists the line that is found. You can abbreviate this command as
rev or ?bash-pattern?.
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One way to examine string data in your script is with the print command (abbreviated p). However a more
versatile print command is x; it can print variable and function definitions and can do arithmetic computations. Finally,
the most general method would be via eval echo.
print expr Use print to display strings as you would from echo. And as such, variable names to be substituted have
to be preceded with a dollar sign. As with echo, filename expansion, e.g. tilde expansion, is performed on unquoted strings. So for
example if you want to print a *, you would write `print "*"', not `print *'. If you want to have the special
characters dollars sign appear, use a backslash.
bashdb<0> print the value of x is $x the value of x is 22 bashdb<1> p The home directory for root is ~root The home directory for root is /root bashdb<2> p '*** You may have won $$$ ***' *** You may have won $$$ *** bashdb<3> # Note the use of the single quotes. bashdb<3> # Compare what happens with double quotes or no quotes |
print p If you omit expr, the BASH debugger displays the last expression again.
x variable1 [variable2...] x expr This is a smarter, more versatile "print" command, and although sometimes it might not be what you want, and you may want to resort
to either print or eval echo....
As with print, if you omit expr, the BASH debugger displays the last expression again.
The x command first checks if expr is variable or a list of variables delimited by spaces. If it is, the
definition(s) and value(s) of each printed via BASH's declare -p command. This will show the variable's
attributes such as if it is read only or if it is an integer. If the variable is an array, that is show and the array values are
printed.
If instead expr is a function, the function definition is printed via BASH's declare -f
command. If expr was neither a variable nor an expression, then we try to get a value via let. And if this
returns an error, as a last resort we call print and give what it outputs.
Since let may be used internally and since (to my thinking) let does funny things, the results may seem
odd unless you understand the sequence tried above and how let works. For "example if the variable foo
has value 5, then `x foo' shows the definition of foo with value 5, and `x foo+5' prints 10 as expected.
So far so good. However if foo is has the value `alpha', `x foo+5' prints 5 because
let has converted the string `alpha' into the numeric value 0. So `p foo+5' will simply print "foo+5";
if you want the value of "foo" substituted inside a string, for example you expect "the value of foo is $foo" to come out "the value
of foo is 5", then the right command to use is print rather than x, making sure you add the dollar onto
the beginning of the variable.
bashdb<0> examine x y
declare -- x="22"
declare -- y="23"
bashdb<1> examine x+y
45
bashdb<2> x fn1
fn1 ()
{
echo "fn1 here";
x=5;
fn3
}
bashdb<2> x FUNCNAME
declare -a FUNCNAME='([0]="_Dbg_cmd_x" [1]="_Dbg_cmdloop" [2]="_Dbg_debug_trap_handler" [3]="main")'
|
V [!][pattern] If you want to all list variables and values or a set of variables by pattern, use this command.
bashdb<0> V dq* dq_args="dq_*" dq_cmd="V" bashdb<1> V FUNCNAME FUNCNAME='([0]="_Dbg_cmd_list_variables" [1]="_Dbg_cmdloop" [2]="_Dbg_debug_trap_handler" [3]="main")' |
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The two most general commands and most "low-level" are eval and shell.
eval e In contrast to the commands of the last section the most general way to examine data is through eval. But you do
much more with this; you can change the values of variables, since, you are just evaluating BASH code.
If you expect output, you should arrange that in the command, such as via echo or printf. For example,
to print the value of foo, you would type `e echo $foo'. This is bit longer than `p $foo' or
(when possible) `x foo'. However suppose you wanted to find out how the builtin test operator `[' works
with the `-z' test condition. You could use eval to do this such as `e [ -z "$foo"] && echo "yes"'.
shell command string !! If you need to execute occasional shell commands during your debugging session, there is no need to leave or suspend the
BASH debugger; you can just use the shell command or its alias !!.
Invoke a shell to execute command string.
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cd Set working directory to directory for debugger and program being debugged. The change does not take effect for the program being debugged until the next time it is started.
pwd Prints the working directory as the program sees things.
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If you find that you want to print the value of an expression frequently (to see how it changes), you might want to add it to the automatic display list so that the BASH debugger evaluates a statement each time your program stops. Each expression added to the list is given a number to identify it; to remove an expression from the list, you specify that number. The automatic display looks like this:
2 (echo $x): 38 |
This display shows item numbers, expressions and their current values.
display expr Add the expression expr to the list of expressions to display each time your program stops.
undisplay dnums� delete display dnums� Remove item numbers dnums from the list of expressions to display.
undisplay does not repeat if you press RET after using it. (Otherwise you would just get the error
`No display number �'.)
disable display dnums� Disable the display of item numbers dnums. A disabled display item is not printed automatically, but is not forgotten. It may be enabled again later.
enable display dnums� Enable display of item numbers dnums. It becomes effective once again in auto display of its expression, until you specify otherwise.
display Display the current values of the expressions on the list, just as is done when your program stops.
info display Print the list of expressions previously set up to display automatically, each one with its item number, but without showing the values. This includes disabled expressions, which are marked as such. It also includes expressions which would not be displayed right now because they refer to automatic variables not currently available.
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You can alter the way BASH interacts with you in various ways given below.
| 4.13.1 Annotation Level (`set annotate') | Annotation Level (set annotate) | |
| 4.13.2 File basename (`set basename') | Show basenames of file names only (set basename) | |
| 4.13.3 Allow Debugging the debugger (`set debugger') | Allow debugging the debugger (set debugger) | |
| 4.13.4 Specifying a Script-File Association (`file') | Specifying a Script-File Associaton (set file) | |
| 4.13.5 Show position information as statements are executed (`set linetrace') | Show position information (set linetrace) | |
| 4.13.6 Logging output (`set logging', `set logging file'...) | Specifying where to write debugger output | |
| 4.13.7 Prompt (`set prompt', `show prompt') | Prompt (set prompt, show prompt) | |
| 4.13.8 Command editing (`set editing', `show editing') | Command editing (set editing, show editing) | |
| 4.13.9 Command Display (`set showcommand') | Command display (set showcommand) | |
| 4.13.10 Command history (`H', `history', `!') | Command history (history, !, H) | |
| 4.13.11 Command Completion (`complete') | Command completion (complete) |
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set annotate integer The annotation level controls how much information the BASH debugger prints in its prompt; right new it just controls whether we show full filenames in output or the base part of the filename without path information. Level 0 is the normal, level 1 is for use when the BASH debugger is run as a subprocess of GNU Emacs of DDD, level 2 is the maximum annotation suitable for programs that control the BASH debugger.
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set basename [ on | 1 ] Source filenames are shown as the basename only. This is useful in running the regression tests.
set basename [ off | 0 ] Source filenames are shown as with their full path. This is the default.
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set debugger [ on | 1 ] Allow the possibility of debugging this debugger. Somewhat of an arcane thing to do. For gurus, and even he doesn't use it all that much.
set debugger [ off | 0 ] Don't allow debugging into the debugger. This is the default.
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Sometimes the BASH debugger gets confused about where to find the script source file for the name reported to
it by bash. To resolve relative file names that bash supplies via BASH_SOURCE, the BASH debugger uses
the current working directory when the debugged script was started as well as the current working directory now (which might be different
if a "cd" command was issued to change the working directory).
However somethimes this doesn't work and there is a way to override this.
file script-file Directs the BASH debugger to use script-file whenever bash would have it refers to the filename
given in BASH_SOURCE. The filename specified in BASH_SOURCE that gets overriden is shown when is this command
is issued.
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BASH has set -x tracing to show commands as they are run. However missing from this is file and line
position information. So the debugger compensates here for what I think is deficiency of BASH by providing this information.
The downside is that this tracing is slower than the built-in tracing of BASH.
The status of whether line tracing is enabled can be show via show linetrace.
set linetrace [ on | 1 ] Turn on line tracing.
set linetrace [ off | 0 ] Turn off line tracing.
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You may want to save the output of the debugger commands to a file. There are several commands to control the debuggers's logging.
set logging set logging [ on | 1 ] Enable or Disable logging.
set logging file filename Change the name of the current logfile. The default logfile is `bashdb.txt'.
set logging overwrite [ on | 1 ] By default, the debugger will append to the logfile. Set overwrite if you want set logging on to overwrite
the logfile instead.
set logging redirect [ on | 1 ] By default, the debugger output will go to both the terminal and the logfile. Set redirect if you want output to
go only to the log file.
show logging Show the current values of the logging settings.
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The BASH debugger indicates its readiness to read a command by printing a string called the prompt. This string is normally:
bashdb${_Dbg_less}${#_Dbg_history[@]}${_Dbg_greater}$_Dbg_space
|
When variables inside the the prompt string are evaluated, the above becomes something like `bashdb<5>' if this is the fifth command executed or perhaps `bashdb<<2>>' if you have called the debugger from inside a debugger session and this is the second command inside the debugger session or perhaps `bashdb<(6)>' if you entered a subshell after the fifth command.
You can change the prompt string with the set prompt command, although it is not normally advisable to do so without
understanding the implications. If you are using the DDD GUI, it changes the changes the prompt and should not do
so. In certain other circumstances (such as writing a GUI like DDD), it may be is useful to change the prompt.
Note: set prompt does not add a space for you after the prompt you set. This allows you to set a prompt which
ends in a space or a prompt that does not. Furthermore due to a implementation limitation (resulting from a limitation of the bash built-in
function "read"), to put a space at the end of the prompt use the `$_Dbg_space' variable.
set prompt newprompt Directs the BASH debugger to use newprompt as its prompt string henceforth.
Warning: changing the prompt can DDD's ability to understand when the debugger is waiting for input.
show prompt Prints a line of the form: `bashdb's prompt is: your-prompt'
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the BASH debugger reads its input commands through bash which uses via the readline interface. This
GNU library provides consistent behavior for programs which provide a command line interface to the user. Advantages
are GNU Emacs-style or vi-style inline editing of commands, csh-like history substitution, and
a storage and recall of command history across debugging sessions.
You may control the behavior of command line editing in BASH with the command set.
set editing set editing [ on | 1 ] Enable command line editing (enabled by default).
set editing [ off | 0 ] Disable command line editing.
show editing Show whether command line editing is enabled.
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The debugger normally lists the line number and source line of the for the statement to be next executed. Often this line contains one expression or one statement and it is clear from this line what's going to happen. However BASH allows many expressions or statements to be put on a single source line; some lines contain several units of execution. Some examples of this behavior are listed below:
x=1; y=2; x=3 (( x > 5 )) && x=5 y=`echo *` |
In the first line of the example above, we have three assignment statements on a single line. In the second line of the example above we have a statement which gets run only if a condition tests true. And in the third line of the example above, we have a command that gets run and then the output of that is substituted in an assignemnt statement. If you were single stepping inside the debugger, each line might get listed more than once before each of the actions that might get performed. (In the case of the conditional statement, the line gets listed only once when the condition is false.)
In order to assist understanding where you are, the enhanced version of BASH maintains a dynamic variable
BASH_COMMAND that contains piece of code next to be run (or is currently being run). The debugger has arranged to save
this and can display this information or not. This is controlled by set showcommand.
set showcommand [auto | on | 1 | off | 0 ] controls whether or not to show the saved BASH_COMMAND for the command next to be executed.
When the value is auto the following heuristic is used to determine whether or not to display the saved BASH_COMMAND.
If the last time you stopped you were at the same place and the command string has changed, then show the command. When the value
on is used, the debugger always shows BASH_COMMAND and when off is used, the debugger nevers
shows BASH_COMMAND. Note that listing the text of the source line is independent of whether or not the command is also
listed.
Some examples:
set showcommand auto This is the default set showcommand on Always show the next command to be executed set showcommand off Never show the next command to be executed |
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The BASH debugger can keep track of the commands you type during your debugging sessions, so that you can be certain of precisely what happened. If the prompt has not been changed (see Prompt), the history number that will be in use next is by default listed in the debugger prompt. Invalid commands and history commands are not saved on the history stack.
H [start-number [end-number]] H [-count] ![-]n:p You can list what is in the history stack with H. Debugger commands in ths history stack are listed from most recent
to least recent. If no start-number is given we start with the most recently executed command and end with the first entry
in the history stack. If start-number is given, that history number is listed first. If end-number is given,
that history number is listed last. If a single negative number is given list that many history commands.
An alternate form is !n:p or !-n:p where n is an integer. If a minus sign
is used, n is taken as the count to go back from the end rather than as a absolute history number. In contrast H,
this form only prints a single history item.
Some examples:
H List entire history H -2 List the last two history items !-2:p List a single history item starting at the same place as above H 5 List history from history number 5 to the begining (number 0) H 5 0 Same as above H 5 3 List history from history number 5 down to history number 3 !5:p List a single history item 5 |
history [[-]n] ![-]n Use this command to reexecute a given history number. If no number is given, the last debugger command in the history is executed.
An alternate form is !n or !-n where n is an integer.
If a minus sign is used in in either form, n is taken as the count to go back from the end rather than as a absolute history number.
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The complete args command lists all the possible completions for the beginning of a command. We can also
show completions for set, show and info subcommands. Use args to specify the beginning
of the command you want completed. For example:
complete d |
results in:
d debug delete disable display deleteall down |
And
complete set a |
results in:
set args set annotate |
This is intended for use by front-ends such as GNU Emacs and DDD.
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There are some front-ends that can use the BASH debugger as a back-end debugger.
| 5.1 Using the BASH debugger from GNU Emacs | ||
| 5.2 Using the BASH debugger from DDD |
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A special interface allows you to use GNU Emacs to view (and edit) the source files for the program you are debugging
with the BASH debugger. However you must be using GNU Emacs version 21 or greater. (M-x show-emacs-version
inside GNU Emacs will tell you what version you are running.)
To use this interface, use the command M-x bashdb in GNU Emacs. Give the executable file you want to debug as an argument. Make sure to use the version that comes with this package as this is newer than that supplied with GNU Emacs.
The bashdb command starts the BASH debugger as a subprocess of Emacs, with input and output through a newly created Emacs buffer.
Using the BASH debugger under Emacs is just like using the BASH debugger normally except for two things:
This applies both to the BASH debugger commands and their output, and to the input and output done by the program you are debugging.
This is useful because it means that you can copy the text of previous commands and input them again; you can even use parts of the output in this way.
All the facilities of GNU Emacs' Shell mode are available for interacting with your script. In particular, you can send signals the usual way--for example, C-c C-c for an interrupt, C-c C-z for a stop.
| 5.1.1 Commands from the GUD buffer | ||
| 5.1.2 Commands from the source script | ||
| 5.1.3 the BASH debugger from a GNU Emacs Shell |
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Each time the BASH debugger displays a stack frame, Emacs automatically finds the source file for that frame and puts an arrow (`=>') at the left margin of the current line. Emacs uses a separate buffer for source display, and splits the screen to show both your the BASH debugger session and the source.
Explicit the BASH debugger list or search commands still produce output as usual, but you probably
have no reason to use them from GNU Emacs.
Warning: If the directory where your script resides is not your current directory, it can be easy to confuse Emacs about the location of the source files, in which case the auxiliary display buffer does not appear to show your source. the BASH debugger can find programs by searching your environment's
PATHvariable, so the the BASH debugger input and output session proceeds normally; but Emacs does not get enough information back from the BASH debugger to locate the source files in this situation. To avoid this problem, either start the BASH debugger mode from the directory where your script resides, or specify an absolute file name when prompted for the M-x gdb argument.A similar confusion can result if you use the the BASH debugger
filecommand to switch to debugging a program in some other location, from an existing the BASH debugger buffer in Emacs.
By default, M-x bashdb calls the bash --debugger. If you need to call the BASH debugger
by a different name (for example, if you keep several configurations around, with different names) you can set the Emacs variable
gud-bashdb-command-name; for example,
(setq gud-bashdb-command-name "bash --debugger") |
(preceded by M-: or ESC :, or typed in the *scratch* buffer, or in your `.emacs' file)
makes Emacs call the program named "bash-debugger" instead.
In the the BASH debugger I/O buffer, you can use the Emacs commands listed below in addition to the standard Shell
mode commands. The I/O buffer name name is usually *gud-script-name*, where script-name
is the name of the script you are debugging.
Many of the commands listed below are also bound to a second key sequence which also can be used in the also be used in the source script. These are listed in Commands from the source script.
Describe the features of Emacs' the BASH debugger Mode.
Execute until exit from the selected stack frame. The Same as the BASH debugger finish command.
The GNU Emacs command name is gud-finish and C-x C-a f C-f is an alternate binding which
also can be used in the source script. See section Finish
(`finish').
Resynchronize the current position with the source window. The GNU Emacs command name is gud-refresh
and C-x C-a C-l is an alternate binding which also can be used in the source script.
Execute to next source line in this function, skipping all function calls. Same as the BASH debugger
next command. The GNU Emacs command name is gud-next and C-x C-a n is an alternate
binding which also can be used in the source script. See section
Next (`next').
With a numeric argument, run that many times. See (Emacs)Arguments section `Numeric Arguments' in The GNU Emacs Manual.
Continue execution of your script Same as the BASH debugger continue command. The GNU
Emacs command name is gud-cont and C-x C-a C-r is an alternate binding which also can be used in the source
script. See Continue (`continue').
Step one source line. Same as the BASH debugger step command. The GNU Emacs command
name is gud-step and C-x C-a C-s is an alternate binding which can be used in the source script. See section
Step (`step').
With a numeric argument, run that many times. See (Emacs)Arguments section `Numeric Arguments' in The GNU Emacs Manual.
Go down a stack frame. Same as the BASH debugger down. With a numeric argument, go down that many
stack frames. See (Emacs)Arguments section `Numeric
Arguments' in The GNU Emacs Manual.
The GNU Emacs command name is gud-down and C-x C-a > is an alternate binding which can
be used in the source script.
Go up a stack frame. With a numeric argument, go up that many stack frames. Same the BASH debugger up
command. See (Emacs)Arguments section `Numeric Arguments'
in The GNU Emacs Manual.
The GNU Emacs command name is gud-up and C-x C-a < is an alternate binding which can
be used in the source script.
Shows argument variables (e.g. $1, $2) of the current stack frame. Same as the BASH
debugger info args command. The GNU Emacs command name is gud-args and C-x C-a a
is an alternate binding which also can be used in the source script.
Restart or run the script. Same as the BASH debugger run command. The GNU Emacs
command name is gud-finish and C-x C-a R is an alternate binding which also can be used in the source script.
Show stack trace. Same as the BASH debugger where command. The GNU Emacs command
name is gud-where and C-x C-a T is an alternate binding which can be used in the source script. See section
Backtraces (`where').
In any source file, the Emacs command C-x SPC (gud-break) tells the BASH debugger to set
a breakpoint on the source line point is on.
If you accidentally delete the source-display buffer, an easy way to get it back is to type the command frame in the
the BASH debugger buffer, to request a frame display; when you run under Emacs, this recreates the source buffer
if necessary to show you the context of the current frame.
The source files displayed in Emacs are in ordinary Emacs buffers which are visiting the source files in the usual way. You can edit the files with these buffers if you wish; but keep in mind that the BASH debugger communicates with Emacs in terms of line numbers. If you add or delete lines from the text, the line numbers that the BASH debugger knows cease to correspond properly with the code.
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tells the BASH debugger to set a breakpoint on the source line point is on. (gud-break)
gud-linetrace
Restart or run the script. Same as the BASH debugger run command. The GNU Emacs
command name is gud-finish. In the corresponding I/O buffer, C-c R is an alternate binding.
Show stack trace. Same as the BASH debugger where command. In the corresponding I/O buffer,
C-c T is an alternate binding. See section
Backtraces (`where').
Go up a stack frame. With a numeric argument, go up that many stack frames. Same the BASH debugger up
command. See (Emacs)Arguments section `Numeric Arguments'
in The GNU Emacs Manual.
The GNU Emacs command name is gud-up. In the corresponding I/O buffer, C-c < is an alternate
binding.
Go down a stack frame. Same as the BASH debugger down. With a numeric argument, go down that many
stack frames. See (Emacs)Arguments section `Numeric
Arguments' in The GNU Emacs Manual.
The GNU Emacs command name is gud-down. In the corresponding I/O buffer, C-c > is an
alternate binding.
gud-tbreak
Step one source line. Same as the BASH debugger step command. See section
Step (`step').
With a numeric argument, run that many times. See (Emacs)Arguments section `Numeric Arguments' in The GNU Emacs Manual.
The GNU Emacs command name is gud-step. In the corresponding I/O buffer, C-c C-s is an
alternate binding.
gud-statement
Restart or run the script. Same as the BASH debugger run command. The GNU Emacs
command name is gud-run. In the corresponding I/O buffer, C-c R is an alternate binding.
Delete breakpoint. gud-remove
gud-print
Execute to next source line in this function, skipping all function calls. Same as the BASH debugger
next command. With a numeric argument, run that many times. See
(Emacs)Arguments section `Numeric Arguments' in
The GNU Emacs Manual.
The GNU Emacs command name is gud-next. In the corresponding I/O buffer, C-c C-n is an
alternate binding.
gud-finish
Continue execution of your script Same as the BASH debugger continue command. The GNU
Emacs command name is gud-cont. In the corresponding I/O buffer, C-c C-r is an alternate binding. See
Continue (`continue').
gud-break
gud-args Shows argument variables (e.g. $1, $2) of the current stack frame. Same as the
BASH debugger info args command. The GNU Emacs command name is gud-args.
In the corresponding I/O buffer, C-c a is an alternate binding which also can be used in the source script.
Move to current position in this source window. The GNU Emacs command name is gud-refresh. In the
corresponding I/O buffer, C-c C-l is an alternate binding.
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It is also possible in GNU emacs to use a regular ("comint") shell and set a mode to watch for the BASH debugger
prompts. To do this, in Emacs issue the command (from M-x) turn-on-bashdbtrack. There is some overhead involved in scanning
output, so if you are not debugging bash programs you probably want to turn this off which can be done via the M-x turn-off-bashdbtrack
command.
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the BASH debugger support is rather new in DDD. As a programming language, the BASH debugger is not feature rich: there are no record structures or hash tables (yet), no pointers, package variable scoping or methods. So much of the data display and visualization features of DDD are disabled.
As with any scripting or interpreted language (e.g. Perl), one can't step by a single machine-language instruction. So the ddd Stepi/Nexti commands are disabled.
Some BASH settings are essential for DDD to work correctly. These settings with their correct values are:
set annotate 1 set prompt set prompt bashdb$_Dbg_less$_Dbg_greater$_Dbg_space |
DDD sets these values automatically when invoking BASH; if these values are changed, there may be some malfunctions.
Pay special attention when the prompt has extra angle brackets (a nested shell) or has any parenthesis (is in a subshell). Quitting may merely exit out of one of these nested (sub)shells rather than leave the program.
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Your bug reports play an essential role in making the BASH debugger reliable.
Reporting a bug may help you by bringing a solution to your problem, or it may not. But in any case the principal function of a bug report is to help the entire community by making the next version of the BASH debugger work better. Bug reports are your contribution to the maintenance of the BASH debugger.
In order for a bug report to serve its purpose, you must include the information that enables us to fix the bug.
| 6.1 Have you found a bug? | ||
| 6.2 How to report bugs |
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If you are not sure whether you have found a bug, here are some guidelines:
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Bug reports can sent via the sourceforge bug tracking mechansim at http://sourceforge.net/tracker/?group_id=61395&atid=497159. Of course patches are very much welcome too. Those can also be sent via the same mechanism.
The fundamental principle of reporting bugs usefully is this: report all the facts. If you are not sure whether to state a fact or leave it out, state it!
Often people omit facts because they think they know what causes the problem and assume that some details do not matter. Thus, you might assume that the name of the variable you use in an example does not matter. Well, probably it does not, but one cannot be sure. Perhaps the bug is a stray memory reference which happens to fetch from the location where that name is stored in memory; perhaps, if the name were different, the contents of that location would fool the debugger into doing the right thing despite the bug. Play it safe and give a specific, complete example. That is the easiest thing for you to do, and the most helpful.
Keep in mind that the purpose of a bug report is to enable us to fix the bug. It may be that the bug has been reported previously, but neither you nor we can know that unless your bug report is complete and self-contained.
Sometimes people give a few sketchy facts and ask, "Does this ring a bell?" Those bug reports are useless, and we urge everyone to refuse to respond to them except to chide the sender to report bugs properly.
To enable us to fix the bug, you should include all these things:
version command.
Without this, we will not know whether there is any point in looking for the bug in the current version of the BASH debugger.
If we were to try to guess the arguments, we would probably guess wrong and then we might not encounter the bug.
Of course, if the bug is that the BASH debugger gets a fatal signal, then we will certainly notice it. But if the bug is incorrect output, we might not notice unless it is glaringly wrong. You might as well not give us a chance to make a mistake.
Even if the problem you experience is a fatal signal, you should still say so explicitly. Suppose something strange is going on, such as, your copy of the BASH debugger is out of synch, or you have encountered a bug in the C library on your system. (This has happened!) Your copy might crash and ours would not. If you told us to expect a crash, then when ours fails to crash, we would know that the bug was not happening for us. If you had not told us to expect a crash, then we would not be able to draw any conclusion from our observations.
The line numbers in our development sources will not match those in your sources. Your line numbers would convey no useful information to us.
Here are some things that are not necessary:
Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it.
This is often time consuming and not very useful, because the way we will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples. We recommend that you save your time for something else.
Of course, if you can find a simpler example to report instead of the original one, that is a convenience for us. Errors in the output will be easier to spot, running under the debugger will take less time, and so on.
However, simplification is not vital; if you do not want to do this, report the bug anyway and send us the entire test case you used.
A patch for the bug does help us if it is a good one. But do not omit the necessary information, such as the test case, on the assumption that a patch is all we need. We might see problems with your patch and decide to fix the problem another way, or we might not understand it at all.
Sometimes with a program as complicated as the BASH debugger it is very hard to construct an example that will make the program follow a certain path through the code. If you do not send us the example, we will not be able to construct one, so we will not be able to verify that the bug is fixed.
And if we cannot understand what bug you are trying to fix, or why your patch should be an improvement, we will not install it. A test case will help us to understand.
Such guesses are usually wrong. Even we cannot guess right about such things without first using the debugger to find the facts.
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The suggestion for a debugger for a Bourne-like shell came from the book "Learning the Korn Shell", by Bill Rosenblatt Copyright (C) 1993 by O'Reilly and Associates, Inc. Others such as Cigy Cyriac, Chet Ramey, Rocky Bernstein, and Gary V. Vaughan expanded and improved on that.
However Bourne-Shell debuggers rely on a signal mechanism (SIGDEBUG) to call a debugger routine. In the Korn shell as
well as BASH in versions prior to 2.05, there was a fundamental flaw: the routine that you registered in the trap, got
called after the statement was executed. It takes little imagination to realize that this is a bit too late to find and correct
errors, especially if the offending command happens to do serious damage like remove filesystems or reboot a server. As a horrible hack,
these debuggers added one to the line number that was just executed on the wishful thinking that this would then be the line of next
statement to execute. Sometimes this was correct, but it was too often wrong, such as in loops and conditionals, comments, or commands
that are continued on the next line.
Another failing of these debuggers was the inability to debug into functions or into sourced files, provide a stack trace, dynamically skip a statement to be run, unconditionally trace into a function or subshell, or stop when a subroutine, sourced file, or subshell completed. In truth, the crux of the problem lay in debugging support in BASH. Given that there was limited bash debugging support, it is not surprising that these debuggers could not do any of the things listed above and could debug only a single shell in a single source file: lines could be listed only from a single text, breakpoints were set into the text which was in fact a copy of the script name prepended with debugger routines.
In version 2.04 of BASH, Rocky Bernstein started hacking on BASH to add call-stack information, source file information, allow for
debugging into functions and for reporting line numbers in functions as relative to the file rather than the beginning of a function
whose origin line number was not accessible from BASH. He started changing the user commands in bashdb to be like other more-advanced
debuggers, in particular perl5db and gdb. However he gave up on this project when realizing that stopping
before a line was crucial. A patch for this was nontrivial and wildly changed semantics. Furthermore the chance of getting his other
patches into BASH was was not going to happen in version 2.04.
In version 2.05, the fundamental necessary change to the semantics of SIGDEBUG trap handling (suggested at least two
years earlier) was made. Also, version 2.05 changed the line-number reporting in a function to be relative to the beginning of the file
rather than the beginning of a function--sometimes. Rocky then picked up where he left off and this then became this debugger. A complete
rewrite of the debugger, some of which started in 2.04 was undertaken. Debugger internals were changed to support multiple file names,
save and restore the calling environment (such as variables $1 and $?) and install debugger signal handlers.
Work was also done on the BASH in conjunction with the debugger to save stack trace information, provide a means for stopping after
a routine finished, debugging into a subshell and so on. And a number of changes were made to BASH just to improve the accuracy of the
line number reporting which is crucial in a debugger.
This documentation was modified from the GNU Debugger (GDB) Reference manual.
Additions to this section are particularly welcome. If you or your friends (or enemies, to be evenhanded) have been unfairly omitted from this list, we would like to add your names!
The following have contributed directly or indrectly to bashdb:
Rocky Bernstein (initial full-featured bashdb with stack tracing and multi-file support)
Masatake YAMATO (help to merge Rocky's hack to the official bash source tree)
Bill Rosenblatt (kshdb), Michael Loukides (kshdb), Cigy Cyriac (proto bashdb), Chet Ramey (proto bashdb), and Gary V. Vaughan (proto bashdb).
Authors of per5ldb:
Ray Lischner, Johan Vromans, and Ilya Zakharevich.
Authors of GDB:
Richard Stallman, Andrew Cagney, Jim Blandy, Jason Molenda, Stan Shebs, Fred Fish, Stu Grossman, John Gilmore, Jim Kingdon, and Randy Smith (to name just a few).
Authors of GUD:
Eric S. Raymond.
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Version 2, June 1991
Copyright � 1989, 1991 Free Software Foundation, Inc. 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. |
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The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.
Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.
Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.
The precise terms and conditions for copying, distribution and modification follow.
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.
You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.
These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.
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In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.
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Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and "any later version", you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.
NO WARRANTY
END OF TERMS AND CONDITIONS
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If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found.
one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
Also add information on how to contact you by electronic and paper mail.
If the program is interactive, make it output a short notice like this when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) year name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details. |
The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program.
You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. signature of Ty Coon, 1 April 1989 Ty Coon, President of Vice |
This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.
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Version 1.1, March 2000
Copyright (C) 2000 Free Software Foundation, Inc. 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. |
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Copyright (C) year your name. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being list their titles, with the Front-Cover Texts being list, and with the Back-Cover Texts being list. A copy of the license is included in the section entitled "GNU Free Documentation License." |
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If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.
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The DJGPP port of the BASH debugger limitations of file names imposed by DOS filesystems.
On DOS/Windows systems, the home directory is the one pointed to by the HOME environment variable.
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