Linux in a Nutshell, Fifth Edition

Patterns and Procedures | 773

gawk

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• BEGIN and END patterns may appear multiple times. The procedures are

merged as if there had been one large procedure.

Except for BEGIN and END, patterns can be combined with the Boolean opera-

tors || (or), && (and), and ! (not). A range of lines can also be specified using

comma-separated patterns:

pattern,pattern

Procedures

Procedures consist of one or more commands, function calls, or variable assign-

ments, separated by newlines or semicolons, and are contained within curly

braces. Commands fall into five groups:

• Variable or array assignments

• Input/Output commands

• Built-in functions

• Control-flow commands

• User-defined functions

Simple Pattern-Procedure Examples

Print first field of each line:

{ print $1 }

Print all lines that contain pattern:

/pattern/

Print first field of lines that contain pattern:

/pattern/ { print $1 }

Select records containing more than two fields:

NF > 2

Interpret input records as a group of lines up to a blank line. Each line is a single

field:

BEGIN { FS = "\n"; RS = "" }

Print fields 2 and 3 in switched order, but only on lines whose first field matches

the string URGENT:

$1 ~ /URGENT/ { print $3, $2 }

Count and print the number of pattern found:

/pattern/ { ++x }

END { print x }

Add numbers in second column and print the total: ...