Command History

Bash keeps a list of the most recently typed commands. This list is the command history.

The easiest way to browse the command history is with the Up and Down arrow keys. The history can also be searched with an exclamation mark (!). This denotes the start of a command name to be completed by Bash. Bash executes the most recent command that matches. For example,

$ date
Wed Apr  4 11:55:58 EDT 2001
$ !d
Wed Apr  4 11:55:58 EDT 2001

If there is no matching command, Bash replies with an event not found error message.

$ !x
bash: !x: event not found

A double ! repeats the last command.

$ date
Thu Jul  5 14:03:25 EDT 2001
$ !!
date
Thu Jul  5 14:03:28 EDT 2001

There are many variations of the ! command to provide shortcuts in specific situations.

A negative number indicates the relative line number. That is, it indicates the number of commands to move back in the history to find the one to execute. !! is the same as !-1.

$ date
Thu Jul  5 14:04:54 EDT 2001
$ printf "%s\n" $PWD
/home/kburtch/
$ !-2
date
Thu Jul  5 14:05:15 EDT 2001

The !# repeats the content of the current command line. (Don't confuse this with #! in shell scripts.) Use this to run a set of commands twice.

$ date ; sleep 5 ; !#
date ; sleep 5 ; date ; sleep 5 ;
Fri Jan 18 15:26:54 EST 2002
Fri Jan 18 15:26:59 EST 2002

Bash keeps the command history in a file called .bash_history unless a variable called HISTFILE is defined. Each time you quit a Bash session, Bash saves the history of your session to the history file. If the histappend shell option is on, the history is appended to the old history up to the maximum allowed size of the history file. Each time you start a Bash session, the history is loaded again from the file.

Another shell option, histverify, enables you to edit the command after it's retrieved instead of executing it immediately.

Bash has a built-in command, history, which gives full control over the command history. The history command with no parameters lists the command history. If you don't want to see the entire history, specify the number of command lines to show.

$ history 10
 1026  set -o emacs
 1027  stty
 1028  man stty
 1029  stty -a
 1030  date edhhh
 1031  date edhhh
 1032  date
 1033  date
 1034  !
 1035  history 10

You can test which command will be matched during a history completion using the -p switch.

$ history -p !d
history -p date
date

A particular command line can be referred to by the line number.

$ !1133
date
Thu Jul  5 14:09:05 EDT 2001

history -d deletes an entry in the history.

$ history -d 1029
$ history 10
 1027  stty
 1028  man stty
 1029  date edhhh
 1030  date edhhh
 1031  date
 1032  date
 1033  !
 1034  history 10
 1035  history -d 1029
 1036  history 10

The -s switch adds new history entries. -w (write) and -r (read) save or load the history from a file, respectively. The -a (append) switch appends the current session history to the history file. This is done automatically when you quit the shell. The -n switch loads the complete history from the history file. history -c (clear) deletes the entire history.

The command history can be searched with !? for the most recent command containing the text. If there is additional typing after the !? search, the command fragment will be delineated with a trailing ?.

$ date
Thu Jul  5 14:12:33 EDT 2001
$ !?ate
date
Thu Jul  5 14:12:38 EDT 2001
$ !?da? '+%Y'
date '+%Y'
2001

The quick substitution history command, ^, runs the last command again, replacing one string with another.

$ date '+%Y'
2001
$ ^%Y^%m^
date '+%m'
07

The Bash history can be turned off by unsetting the -o history shell option. The cmdhist option saves multiple line commands in the history. The lithist option breaks up commands separated by semicolons into separate lines.

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