I used to (before use strict) compose regexps by hiding the components inside an if, e.g.:
$complex_re = /^($ip) ($host) ($msg)$/ if ( $ip = /\d+\.\d+\.\d+\.\d+/, $host = /[\-\.\w]+/, $msg = /.*/ );
Nowadays, I use strict and eval, e.g.
my $complex_re = eval { my $ip = qr/\d+\.\d+\.\d+\.\d+/; my $host = qr/[\-\.\w]+/; my $msg = qr/.*/; return /^($ip) ($host) ($msg)$/; );
We pay about a 5% penalty for the eval when we use this in a tight loop, however we can solve that by moving the regexp creation outside the loop.
Rate with eval without eval with eval 116279/s -- -5% without eval 121951/s 5% --

In reply to Regexp Legibility by patrickhaller
in thread Regexp do's and don'ts by muba

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