Question

Does Perl support conditional regular expression :

(?(condition)true-pattern|false-pattern)

i.e. if the condition is true then try to match the true pattern else try to match the false pattern

If Perl supported conditional regular expressions then why didn’t this code print 1?

use strict;
use warnings;

$_ = 'AB';

if ( /(?(A)B|C)/ ) {
  print 1;
}

Answer 1

Perl supports conditional patterns.

Your regex doesn’t just not match, it throws the following syntax error:

Unknown switch condition (?(A) in regex; marked by <-- HERE in m/(?( <-- HERE A)B|C)/

That’s because A is not a valid condition.