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awk

Introduction​

This cheat sheet provides a quick reference for some common awk commands and concepts. awk is a powerful text-processing tool used in Unix-like operating systems for data extraction and manipulation.

AWK Concepts​

Basic Structure​

An AWK script consists of patterns and actions. When a pattern matches a line of input, the associated action is executed.

pattern { action }

Fields​

AWK divides input lines into fields, which are separated by whitespace (by default). You can access fields using $1, $2, and so on.

  • Print the first field of each line:
    awk '{ print $1 }' file.txt

Built-in Variables​

AWK provides several built-in variables, such as NF (number of fields) and NR (record number).

  • Print the number of fields in each line:
    awk '{ print NF }' file.txt

Regular Expressions​

AWK supports regular expressions for pattern matching.

  • Print lines containing the word "pattern":
    awk '/pattern/ { print }' file.txt

BEGIN and END Blocks​

The BEGIN block is executed before processing any input, and the END block is executed after processing all input.

  • Calculate the sum of values in a column:
    awk 'BEGIN { sum = 0 } { sum += $1 } END { print sum }' file.txt

Conditional Statements​

AWK supports conditional statements like if and else.

  • Print lines with values greater than a threshold:
    awk '{ if ($1 > threshold) print }' file.txt

Functions​

AWK provides built-in functions for string and numeric operations.

  • Convert all text to uppercase:
    awk '{ print toupper($0) }' file.txt

User-Defined Variables​

You can define and use user-defined variables in AWK scripts.

  • Print the sum of values and a custom message:
    awk '{ sum += $1 } END { print "Sum:", sum }' file.txt

AWK Command-Line​

  • Execute an AWK script from a file:

    awk -f script.awk file.txt

  • Print specific fields from a file (space-separated):

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

  • Process multiple input files:

    awk '{ print FILENAME, $0 }' file1.txt file2.txt

Conclusion​

This cheat sheet covers some common awk commands and concepts. awk is a versatile text-processing tool for data extraction and manipulation in Unix-like environments; refer to the official AWK documentation for more in-depth information and advanced usage.