Defining a Range of Lines in Ed

You can use line numbers to explicitly define a line or range of lines. Addresses that use explicit numbers are called absolute line addresses. For example:

To make editing with line numbers easier, you can also display all line numbers on the left of the screen. The command:

:set number

or its abbreviation:

:set nu

displays line numbers. The file practice then appears:

1  With a screen editor
  2  you can scroll the page,
  3  move the cursor, delete lines,
  4  insert characters and more

The displayed line numbers are not saved when you write a file, and they do not print if you print the file. Line numbers are displayed either until you quit the vi session or until you disable the set option:

:set nonumber

or:

:set nonu

To temporarily display the line numbers for a set of lines, you can use the # sign. For example:

:1,10#

would display the line numbers from line one to line ten.

You can also use the CTRL-G command to display the current line number. You can thus identify the line numbers corresponding to the start and end of a block of text by moving to the start of the block, typing CTRL-G, then moving to the end of the block and typing CTRL-G again.

Yet another way to identify line numbers is with the ex = command:

:=

Print the total number of lines.

 

:.=

Print the line number of the current line.

 

:/ pattern/=

Print the line number of the first line that matches pattern.

Line Addressing Symbols

You can also use symbols for line addresses. A dot (.) stands for the current line; $ stands for the last line of the file. % stands for every line in the file; it's the same as the combination 1,$. These symbols can also be combined with absolute line addresses. For example:

 

:.,$d

Delete from current line to end of file.

 

:20,.m$

Move from line 20 through the current line to the end of the file.

 

:%d

Delete all the lines in a file.

:%t$

Copy all lines and place them at the end of the file (making a consecutive duplicate).

In addition to an absolute line address, you can specify an address relative to the current line. The symbols + and - work like arithmetic operators. When placed before a number, these symbols add or subtract the value that follows. For example:

:.,.+20d

Delete from current line through the next 20 lines.

 

:226,$m.-2

Move lines 226 through the end of the file to two lines above the current line.

 

:.,+20#

Display line numbers from the current line to 20 lines further on in the file.

In fact, you don't need to type the dot (.) when you use + or -, because the current line is the assumed starting position.

Without a number following them, + and - are equivalent to +1 and -1, respectively.^[2] Similarly, ++ and -- each extend the range by an additional line, and so on. The + and - can also be used with search patterns, as shown in the next section.

^[2] In a relative address, you shouldn't separate the plus or minus symbol from the number that follows it. For example, +10 means "10 lines following," but + 10 means "11 lines following (1 + 10)," which is probably not what you mean (or want).

The number 0 stands for the top of the file (imaginary line 0). 0 is equivalent to 1-, and both allow you to move or copy lines to the very start of a file, before the first line of existing text. For example:

 

:-,+t0

Copy three lines (the line above the cursor through the line below the cursor) and put them at the top of the file.

Search Patterns

Another way that ex can address lines is by using search patterns. For example:

:/ pattern/d

Delete the next line containing pattern.

: /pattern/+d

Delete the line below the next line containing pattern. (You could also use +1 instead of + alone.)

: /pattern1/,/ pattern2/d

Delete from the first line containing pattern1 through the first line containing pattern2.

:.,/ pattern/m23

Take the text from the current line (.) through the first line containing pattern and put it after line 23.

Note that patterns are delimited by a slash both before and after.

If you make deletions by pattern with vi and ex, there is a difference in the way the two editors operate. Suppose your file practice contains the lines:

The vi delete to pattern command deletes from the cursor up to the word while, but leaves the remainder of both lines. :.,/while/d  

The ex command deletes the entire range of addressed lines; in this case both the current line and the line containing the pattern. All lines are deleted in their entirety.

Redefining the Current Line Position

Sometimes, using a relative line address in a command can give you unexpected results. For example, suppose the cursor is on line 1, and you want to print line 100 plus the five lines below it. If you type:

:100,+5 p
 

you'll get an error message saying, "First address exceeds second." The reason the command fails is that the second address is calculated relative to the current cursor position (line 1), so your command is really saying this:

:100,6 p

What you need is some way to tell the command to think of line 100 as the "current line," even though the cursor is on line 1.

ex provides such a way. When you use a semicolon instead of a comma, the first line address is recalculated as the current line. For example, the command:

:100;+5 p

prints the desired lines. The +5 is now calculated relative to line 100. A semicolon is useful with search patterns as well as absolute addresses. For example, to print the next line containing pattern, plus the 10 lines that follow it, enter the command:

:/pattern/;+10 p
 

Global Searches

You already know how to use / (slash) in vi to search for patterns of characters in your files. ex has a global command, g, that lets you search for a pattern and display all lines containing the pattern when it finds them. The command :g! does the opposite of :g. Use :g! (or its synonym :v) to search for all lines that do not contain pattern.

You can use the global command on all lines in the file, or you can use line addresses to limit a global search to specified lines or to a range of lines.

:g/ pattern

Finds (moves to) the last occurrence of pattern in the file.

:g/ pattern/p

Finds and displays all lines in the file containing pattern.

:g!/ pattern/nu

Finds and displays all lines in the file that don't contain pattern; also displays the line number for each line found.

:60,124g/ pattern/p

Finds and displays any lines between lines 60 and 124 containing pattern.

As you might expect, g can also be used for global replacements. We'll talk about that in Chapter 6.

Combining ex Commands

You don't always need to type a colon to begin a new ex command. In ex, the vertical bar (|) is a command separator, allowing you to combine multiple commands from the same ex prompt (in much the same way that a semicolon separates multiple commands at the UNIX shell prompt). When you use the |, keep track of the line addresses you specify. If one command affects the order of lines in the file, the next command does its work using the new line positions. For example:

:1,3d | s/thier/their/

Delete lines 1 through 3 (leaving you now on the top line of the file); then make a substitution on the current line (which was line 4 before you invoked the ex prompt).

:1,5 m 10 | g/pattern/nu

Move lines 1 through 5 after line 10, and then display all lines (with numbers) containing pattern.

Note the use of spaces to make the commands easier to read.

Global Replacement

Sometimes, halfway through a document or at the end of a draft, you may recognize inconsistencies in the way that you refer to certain things. Or, in a manual, some product whose name appears throughout your file is suddenly renamed (marketing!). Often enough it happens that you have to go back and change what you've already written, and you need to make the changes in several places.

The way to make these changes is with a powerful change command called global replacement. With one command you can automatically replace a word (or a string of characters) wherever it occurs in the file.

In a global replacement, the ex editor checks each line of a file for a given pattern of characters. On all lines where the pattern is found, ex replaces the pattern with a new string of characters. For right now, we'll treat the search pattern as if it were a simple string; later in the chapter we'll look at the powerful pattern-matching language known as regular expressions.

Global replacement really uses two ex commands: :g (global) and :s (substitute). Since the syntax of global replacement commands can get fairly complex, let's look at it in stages.

The substitute command has the syntax:

:s/old/new/

This changes the first occurrence of the pattern old to new on the current line. The / (slash) is the delimiter between the various parts of the command. (The slash is optional when it is the last character on the line.)

A substitute command with the syntax:

:s/old/new/g
 

changes every occurrence of old to new on the current line, not just the first occurrence. The :s command allows options following the substitution string. The g option in the syntax above stands for global. (The g option affects each pattern on a line; don't confuse it with the :g command, which affects each line of a file.)

By prefixing the :s command with addresses, you can extend its range to more than one line. For example, this line will change every occurrence of old to new from line 50 to line 100:

:50,100s/old/new/g
 

This command will change every occurrence of old to new within the entire file:

:1,$s/old/new/g
 

You can also use % instead of 1,$ to specify every line in a file. Thus the last command could also be given like this:

:%s/old/new/g
 

Global replacement is much faster than finding each instance of a string and replacing it individually. Because the command can be used to make many different kinds of changes, and because it is so powerful, we will first illustrate simple replacements and then build up to complex, context-sensitive replacements.

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