Filter Commands
Introduction
Several utilities are available to manipulate and filter files. Three of the more common utilites are discussed
here: grep, sed and awk.
For further explanation of grep, see the ITS documentation at The Grep Command.
Sed
The sed utility copies the named filename to the standard output, edited according to a
script of commands.
sed -e <script> <filename>
Here is an example of a <script> command:
sed -e s/<expression>/<replacement>/g
<filename>
Example: sed -e s/dog/wolf/g animals
In this example, sed will substitute all the occurances of "dog" with
"wolf" in the file called animals.
If the expression contains a space, surround it with quotation marks as shown in the example below:
Example: sed -d s/"wild dog"/wolf/g animals
Here is another example of a <script> command:
sed -e y/<string1>/<string2>/ <filename>
Example: sed -e y/unix/UNIX/ animals
In this example, sed will transform all the occurances of "unix" into "UNIX". The variables <string1> and <string2> must have the same number of characters.
For more examples of <script> commands and for more information on sed, type
man sed.
Awk
The awk utility scans each input file for lines that match any of a set of patterns
specified. For each pattern specified there may be an associated action performed.
awk '<pattern> {<action>}' <filename>
The following example will print to the screen every line which contains the pattern "dog" in the file named
animals.
Example: awk '/dog/ {print}' animals
This next example will print "Found It" to the screen for every line which starts with the pattern "Tiger" in the file
named animals.
Example: awk '/^Tiger/ {print "Found It"}' animals
awk is a very powerful and complex utility. For more information on awk,
type man awk.
Last updated:
February 03, 2011