Awk
Overview
What is
'awk'?
Invoking 'awk'
Naming the fields
Formatted output
Operators used
by Awk
Patterns
Variables
Accessing
Values
Special
variables
Arguments to 'awk'
scripts
Arrays
Field and record
separators
Functions
List of Awk
functions
Summary
Exercises
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Naming the fields
In a shell script, $1, $2, etc., name
the arguments of the script, but in an Awk script $1,
$2, etc., name the fields of each record of data. The
whole record is referred to as $0. To cause Awk to
display something on standard output the command print
can be used. Whenever the action print is performed, a
Newline character is always displayed afterwards, just
like the shell command echo. The following script
copies standard input to standard output:
{ print $0 }
Worked example
Write a shell script to run Awk to display the first field of
each line of standard input.
Solution: The Awk script is simple for this task,
so we can enclose it within single quotes in the shell script. The
Awk action is print $1 to be performed on each
line. The Awk pattern to match every line is the null pattern, so
that the Awk script becomes
{ print $1 }
To run Awk from a shell script, we require the utility
awk, followed by this script (enclosed in quotes).
Don't forget the comments!
# This shell script prints the first field of each
# line of standard input
awk '{ print $1 }'
If you give print several arguments, it will
concatenate their values before displaying them. The following Awk
script displays each line of input enclosed in parentheses:
{ print "(" $0 ")" }
so for input
hello there
Chris
the output would be:
(hello there)
(Chris)
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