Linux Know-How provides a collection of introductory texts on often needed Linux skills.

Non-interactive editing

Reading sed commands from a file

Multiple sed commands can be put in a file and executed using the -f option. When creating such a file, make sure that:

  • No trailing white spaces exist at the end of lines.

  • No quotes are used.

  • When entering text to add or replace, all except the last line end in a backslash.

Writing output files

Writing output is done using the output redirection operator >. This is an example script used to create very simple HTML files from plain text files.

sandy ~> cat script.sed
<head><title>sed generated html</title></head>\
<body bgcolor="#ffffff">\

sandy ~> cat

# This is a simple script that you can use for converting text into HTML.
# First we take out all newline characters, so that the appending only happens
# once, then we replace the newlines.

echo "converting $1..."

sed "s/\n/^M/" $1 | sed -f $SCRIPT | sed "s/^M/\n/" > $TEMPFILE

echo "done."

sandy ~>

$1 holds the first argument to a given command, in this case the name of the file to convert:

sandy ~> cat test

More on positional parameters in Chapter 7.

sandy ~> test
converting test...

sandy ~> cat test
<head><title>sed generated html</title></head>
<body bgcolor="#ffffff">

sandy ~>

This is not really how it is done; this example just demonstrates sed capabilities. See Section 6.3 for a more decent solution to this problem, using awk BEGIN and END constructs.

NoteEasy sed

Advanced editors, supporting syntax highlighting, can recognize sed syntax. This can be a great help if you tend to forget backslashes and such.

Last Update: 2010-12-16