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Awk
Awk is a programming language designed for text processing and data extraction. It was created in the 1970s and remains widely used today for tasks such as filtering and transforming text data, generating reports, and performing basic calculations. Awk is known for its simplicity and versatility, making it a popular tool for Unix system administrators and data analysts.
Invocation
We can use awk directly in stdin or we can reference .awk files for more elaborate scripts
# CLI
awk [program] file1, file2, file3
# Script file
awk -f [ref_to_script_file] file1, file2, file3
We can also obviously pipe to it.
Syntactic structure
An awk program consists in a sequence of pattern-action statements and optional functional definitions. awk is line-oriented.
Patterns and actions
The basic structure of an awk script is as follows:
pattern {action}
A pattern is what you want to match against. It can be a literal string or a regex. The action is what process you want to execute against the lines in the input that match the pattern.
The following script prints each line of input that contains the word "error":
/error/ {print} file.tx
/error/ is the patttern and {print} is the action.
Lines, records, fields
When awk receives a file it divides the lines into records.
Each line awk receives is broken up into a sequence of fields.
The fields are accessed by special variables:
-
$1reads the first field,$2reads the second field and so on. -
The variable
$0refers to the whole recordk
Patterns and actions
Variables
Variables are denoted with a leading $. The fields of input are denoted sequentially with $1, $2, $3...
This script prints the first and third fields of each line of input:
{ print $1, $2 }