AWK

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Index

Structure

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awk 'BEGIN{ACTION} PATTERN{ACTION} END{ACTION}'

Printing

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awk 'BEGIN{print "hello", "world"}'   # hello world
awk 'BEGIN{print "hello" "world"}'   # helloworld
awk 'BEGIN{print "hello"; print "world"}'   # hello\nworld
awk 'BEGIN{printf "%s","hello"; printf "%s","world"}'   # helloworld

Using bash variable inside awk

Quoting

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#!/bin/bash

var=4
awk 'BEGIN{print '$var'}'

Commandline

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#!/bin/bash

var=4
awk -v v=$var 'BEGIN{print v}'
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#!/bin/bash

var=4
car=5
awk -v v=$var -v c=$car 'BEGIN{print v,c}'

Summary of programming constructs in awk

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if ( conditional ) statement [ else statement ]
while ( conditional ) statement
for ( expression ; conditional ; expression ) statement
for ( variable in array ) statement
break
continue
{ [ statement ] ...}
variable=expression
print [ expression-list ] [ > expression ]
printf format [ , expression-list ] [ > expression ]
next
exit

Example:

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#!/bin/bash

echo "AWK example:"

awk '
BEGIN{
    start=1;
    end=10;

    for(i=start; i <= end; i++) {
        if (i % 2 == 0) {
            print i;
        }
    }
}
'

Regular Expression match

~ can be used to check if a string matches a regular expression. And !~ will evaluate to true if a string
doesn’t match with a regular expression.

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#!/bin/bash

awk 'BEGIN{word="other";if(word ~ /the/){print "match"}}'

AWK builtin variables

  • FS - Input field seperator
  • OFS - Output field seperator
  • RS - Inpute record field seperator
  • ORS - Output record field seperator
  • NF - Number of fields/columns
  • NR - record number/line number
  • FILENAME - Name of the file being read