Bash-Beginners-Guide

Bash Guide for Beginners
The field separator is represented by the built-in variable FS. Note that this is something different from the
IFS variable used by POSIX-compliant shells.
The value of the field separator variable can be changed in the awk program with the assignment operator =.
Often the right time to do this is at the beginning of execution before any input has been processed, so that the
very first record is read with the proper separator. To do this, use the special BEGIN pattern.
In the example below, we build a command that displays all the users on your system with a description:
kelly is in ~> awk 'BEGIN { FS=":" } { print $1 "\t" $5 }' /etc/passwd
--output omitted--
kelly Kelly Smith
franky Franky B.
eddy Eddy White
willy William Black
cathy Catherine the Great
sandy Sandy Li Wong
kelly is in ~>
In an awk script, it would look like this:
kelly is in ~> cat printnames.awk
BEGIN { FS=":" }
{ print $1 "\t" $5 }
kelly is in ~> awk -f printnames.awk /etc/passwd
--output omitted--
Choose input field separators carefully to prevent problems. An example to illustrate this: say you get input in
the form of lines that look like this:
"Sandy L. Wong, 64 Zoo St., Antwerp, 2000X"
You write a command line or a script, which prints out the name of the person in that record:
awk 'BEGIN { FS="," } { print $1, $2, $3 }' inputfile
But a person might have a PhD, and it might be written like this:
"Sandy L. Wong, PhD, 64 Zoo St., Antwerp, 2000X"
Your awk will give the wrong output for this line. If needed, use an extra awk or sed to uniform data input
formats.
The default input field separator is one or more whitespaces or tabs.
6.3.2. The output separators
6.3.2.1. The output field separator
Fields are normally separated by spaces in the output. This becomes apparent when you use the correct syntax
for the print command, where arguments are separated by commas:
kelly@octarine ~/test> cat test
Chapter 6. The GNU awk programming language 74