bash Cookbook

Keeping Some Output, Discarding the Rest

Problem

You need a way to keep some of your output and discard the rest.

Solution

The following code prints the first word of every line of input:

$ awk '{print $1}' myinput.file

Words are delineated by whitespace. The awk utility reads data from the filename supplied on the command line, or from standard input if no filename is given. Therefore, you can redirect the input from a file, like this:

$ awk '{print $1}' < myinput.file

or even from a pipe, like this:

$ cat myinput.file | awk '{print $1}'

Discussion

The awk program can be used in several different ways. Its easiest, simplest use is just to print one or more selected fields from its input.

Fields are delineated by whitespace (or specified with the -F option) and are numbered starting at 1. The field $0 represents the entire line of input.

awk is a complete programming language; awk scripts can become extremely complex. This is only the beginning.

See Also

• Cutting Out Parts of Your Output

• Isolating Specific Fields in Data

• man awk

• http://www.faqs.org/faqs/computer-lang/awk/faq/

• Effective awk Programming by Arnold Robbins (O’Reilly)

• sed & awk by Arnold Robbins and Dale Dougherty (O’Reilly)