awk

Overview

The awk command is a powerful text processing language for pattern scanning and processing. It treats input as records and fields, making it ideal for structured text manipulation.

Syntax

awk [options] 'program' [input-file]

Common Options

Option Description
-F fs Field separator
-f file Program file
-v var=val Set variable
-W version Show version
-W help Show help
-W lint Check syntax
-W exec Execute only
-W compat Compatibility
-W copyleft Show license
-W usage Show usage

Built-in Variables

Variable Description
$0 Entire line
$1-$n Field number
NF Number of fields
NR Record number
FS Field separator
RS Record separator
OFS Output field sep
ORS Output record sep
FILENAME Current file
FNR File record number

Key Use Cases

  1. Field processing
  2. Text analysis
  3. Report generation
  4. Data extraction
  5. File transformation

Examples with Explanations

Example 1: Print Fields

awk '{print $1, $3}' file

Print first and third fields

Example 2: Field Separator

awk -F: '{print $1}' /etc/passwd

Print usernames from passwd

Example 3: Pattern Match

awk '/pattern/ {print}' file

Print matching lines

Common Usage Patterns

  1. Sum column:

    awk '{sum += $1} END {print sum}'

  2. Count matches:

    awk '/pattern/ {count++} END {print count}'

  3. Format output:

    awk '{printf "%-10s %s\n", $1, $2}'

Programming Features

  1. Variables
  2. Arrays
  3. Functions
  4. Control flow
  5. Regular expressions

Additional Resources

Best Practices

  1. Use functions
  2. Comment code
  3. Test patterns
  4. Handle errors
  5. Document usage

Common Functions

  1. length()
  2. substr()
  3. index()
  4. match()
  5. split()

Troubleshooting

  1. Field separation
  2. Pattern matching
  3. Variable scope
  4. Syntax errors
  5. File handling