awk

awk is a language for text parsing and manipulation, it’s often used as a tokenizer in bash pipes but it can do a lot more of that

before starting i write down the most common use case of awk

some_command_that_prints_on_stdout | awk -F'[SEPARATOR]'  '{print $[FIELD]}'

Processing model

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awk starts by loading user defined functions than execute BEGIN block that process text one record at a time (default behavior is line filter) :

flowchart TD
A[load functions]
B[initial setup\n by running the BEGIN block]
C[read line]
D[process line]
E[clean up\by running END block]
A --> B --> C
C --> D
D --> C
D --> E

Syntax

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Blocks are delimited by {} each line contains an isntruction, instructoins can be separated by ;

BEGIN{  }
{  }
END{  }

Regex filters and ~ operator

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lines can be regex parsed using a variable with a regular expression and then filter the input using the ~ operator

BEGIN{
filter="REGEX"
}


$0 ~ filter{
    # operation on matched records
}

Match function

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match regex element and put beckrefs in an array

    match($0, /.* — (.*) ft\. .*/, arr)
    print arr[1]

Oneliners

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• print all token except first one

awk '{$1=""; print $0}'