Multiple commands syntax (sed, a stream editor)

3.8 Multiple commands syntax

There are several methods to specify multiple commands in a sed program.

Using newlines is most natural when running a sed script from a file (using the -f option).

On the command line, all sed commands may be separated by newlines. Alternatively, you may specify each command as an argument to an -e option:

$ seq 6 | sed '1d
3d
5d'
2
4
6

$ seq 6 | sed -e 1d -e 3d -e 5d
2
4
6

A semicolon (‘;’) may be used to separate most simple commands:

$ seq 6 | sed '1d;3d;5d'
2
4
6

The {,},b,t,T,: commands can be separated with a semicolon (this is a non-portable GNU sed extension).

$ seq 4 | sed '{1d;3d}'
2
4

$ seq 6 | sed '{1d;3d};5d'
2
4
6

Labels used in b,t,T,: commands are read until a semicolon. Leading and trailing whitespace is ignored. In the examples below the label is ‘x’. The first example works with GNU sed. The second is a portable equivalent. For more information about branching and labels see Branching and flow control.

$ seq 3 | sed '/1/b x ; s/^/=/ ; :x ; 3d'
1
=2

$ seq 3 | sed -e '/1/bx' -e 's/^/=/' -e ':x' -e '3d'
1
=2

3.8.1 Commands Requiring a newline

The following commands cannot be separated by a semicolon and require a newline:

a,c,i (append/change/insert)

All characters following a,c,i commands are taken as the text to append/change/insert. Using a semicolon leads to undesirable results:

$ seq 2 | sed '1aHello ; 2d'
1
Hello ; 2d
2

Separate the commands using -e or a newline:

$ seq 2 | sed -e 1aHello -e 2d
1
Hello

$ seq 2 | sed '1aHello
2d'
1
Hello

Note that specifying the text to add (‘Hello’) immediately after a,c,i is itself a GNU sed extension. A portable, POSIX-compliant alternative is:

$ seq 2 | sed '1a\
Hello
2d'
1
Hello

# (comment)

All characters following ‘#’ until the next newline are ignored.

$ seq 3 | sed '# this is a comment ; 2d'
1
2
3


$ seq 3 | sed '# this is a comment
2d'
1
3

r,R,w,W (reading and writing files)

The r,R,w,W commands parse the filename until end of the line. If whitespace, comments or semicolons are found, they will be included in the filename, leading to unexpected results:

$ seq 2 | sed '1w hello.txt ; 2d'
1
2

$ ls -log
total 4
-rw-rw-r-- 1 2 Jan 23 23:03 hello.txt ; 2d

$ cat 'hello.txt ; 2d'
1

Note that sed silently ignores read/write errors in r,R,w,W commands (such as missing files). In the following example, sed tries to read a file named ‘hello.txt ; N’. The file is missing, and the error is silently ignored:

$ echo x | sed '1rhello.txt ; N'
x

e (command execution)

Any characters following the e command until the end of the line will be sent to the shell. If whitespace, comments or semicolons are found, they will be included in the shell command, leading to unexpected results:

$ echo a | sed '1e touch foo#bar'
a

$ ls -1
foo#bar

$ echo a | sed '1e touch foo ; s/a/b/'
sh: 1: s/a/b/: not found
a

s///[we] (substitute with e or w flags)

In a substitution command, the w flag writes the substitution result to a file, and the e flag executes the subsitution result as a shell command. As with the r/R/w/W/e commands, these must be terminated with a newline. If whitespace, comments or semicolons are found, they will be included in the shell command or filename, leading to unexpected results:

$ echo a | sed 's/a/b/w1.txt#foo'
b

$ ls -1
1.txt#foo