Mastering Modern Perl: Writing Efficient and Maintainable Code/

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Grouping and Alternation

Grouping and Alternation

Learn about grouping and alternation in Perl.

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Grouping

Previous examples have all applied quantifiers to simple atoms. We may apply them to any regex element:

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use Test::More;
my $pork = qr/pork/;
my $beans = qr/beans/;
like 'pork and beans', qr/\A$pork?.*?$beans/,
     'maybe pork, definitely beans';
done_testing();

If we expand the regex manually, the results may surprise us:

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use Test::More;
my $pork_and_beans = qr/\Apork?.*beans/;
like 'pork and beans', qr/$pork_and_beans/,
     'maybe pork, definitely beans';
like 'por and beans', qr/$pork_and_beans/,
     'wait... no phylloquinone here!';
     
done_testing();

Sometimes, specificity helps pattern accuracy:

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use Test::More;
my $pork = qr/pork/;
my $and = qr/and/;
my $beans = qr/beans/;
like 'pork and beans', qr/\A$pork? $and? $beans/,
     'maybe pork, maybe and, definitely beans';
done_testing();

Alternation

Some ...