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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.

Awk Usage Overview

awk [options] [program] [file...]

Option	Description
`-F fs`	Set the input field separator to `fs`
`-v var=value`	Assign a value to an awk variable before program execution
`-f file`	Read the awk program from the specified `file`
`program`	Provide the awk program directly as a quoted string
`file...`	One or more input files; if omitted, reads from standard input

Note

Always quote your program (single or double quotes) so the shell passes it verbatim to awk.

For full details, see the GNU Awk Manual.

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
$

Warning

Without quotes around {}, many shells will interpret braces or special characters—always quote your action blocks!

The `print` Statement

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

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

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

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

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

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 }'
```

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

Links and References

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