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Awk is a powerful, domain-specific language built for efficient text processing. In this guide, we’ll cover its core syntax, the pattern-action structure, and how to use the print statement to extract and format data.

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Awk Usage Overview

awk [options] [program] [file...]
OptionDescription
-F fsSet the input field separator to fs
-v var=valueAssign a value to an awk variable before program execution
-f fileRead the awk program from the specified file
programProvide the awk program directly as a quoted string
file...One or more input files; if omitted, reads from standard input
Always quote your program (single or double quotes) so the shell passes it verbatim to awk.
For full details, see the GNU Awk Manual.

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Pattern-Action Structure

An awk program is a sequence of pattern-action pairs: 
pattern { action }
  • If pattern is omitted, action runs on every input line.
  • The { … } block is the action block, containing commands like print, loops, and conditionals.
Example: Start an interactive session that does nothing with your input. 
awk '{}'
Type lines, then press Ctrl-D to end input: 
$ awk '{}'
hello world
^D
$
Without quotes around {}, many shells will interpret braces or special characters—always quote your action blocks!

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The print Statement

Inside the action block, print sends its arguments (fields, string literals, variables) to standard output.

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Accessing Fields

By default, awk splits each line on whitespace into fields named $1, $2, …, $NF. 
$ awk '{ print $2 }'
abc def ghi
jkl mno pqr
^D
def
mno

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Processing Files

Place the filename after the program to read from a file instead of interactively: Given abc.txt: 
abc def ghi
jkl mno pqr
xy yz uv
Run: 
awk '{ print $3 }' abc.txt
Output: 
ghi
pqr
uv

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Printing String Literals

You can mix fields and literal strings in a single print: 
awk '{ print "Line:", $1, "->", $NF }' abc.txt
Output: 
Line: abc -> ghi
Line: jkl -> pqr
Line: xy -> uv

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Multiple Expressions

Separate expressions by commas; awk joins them with the output field separator (OFS, default is a space): 
awk '{ print "Hello", "World" }' abc.txt

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Redirecting and Piping Input

Awk accepts input from:
  • Files: 
    awk '{ print $0 }' data.txt
  • Standard input via redirection: 
    awk '{ print $0 }' < data.txt
  • Piping from other commands: 
    cat data.txt | awk '{ print $1 }'

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Summary

  • Command structure: awk [options] [pattern-action] [file...]
  • Pattern-action: pattern { action }
  • Fields: $1, $2, … $NF
  • String literals: printed as-is within quotes
  • Separators: input (FS) and output (OFS)
  • Interactive mode: omit files; end with Ctrl-D, cancel with Ctrl-C

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