wintermte has asked for the wisdom of the Perl Monks concerning the following question:

Monks, I can't seem to find a way to do this. I would like to be able to specify the modifiers of a regular expression via a scalar. For example: 
my $modifiers = 'i';
my $text = 'abc';

if ( $text =~ m/$pattern/$modifiers)
{
   print "it matches\n";
}

[download]
The perl interpreter obviously doesn't like this because it is expecting an operator instead of the scalar $modifiers. Is there a way to do this other than a big if elsif statement that covers all of the various operators that may be in $modifiers? Using qr doesn't work any better to build the expression. Thanks in advance.

Replies are listed 'Best First'.
Re: Regular expression modifiers in a scalar
by Sidhekin (Priest) on Jul 24, 2006 at 03:20 UTC

    You want modifiers inside the regex: 

    my $modifiers = 'i';
my $text = 'abc';

my $pattern = 'BC';

if ( $text =~ m/(?$modifiers:$pattern)/) {
   print "it matches\n";
}

    [download]

    Only good for turning on (or off) options imsx. See perlre.

    print "Just another Perl ${\(trickster and hacker)},"
    The Sidhekin proves Sidhe did it!

[reply]
[d/l]
[select]
      Excellent. That is exactly what I was looking for! Thanks for the quick reply.
[reply]
Re: Regular expression modifiers in a scalar
by Zaxo (Archbishop) on Jul 24, 2006 at 03:31 UTC

    The problem seems to be that $modifiers is not interpolated in time for the compiled regex to have seen it. This will work, 

    if ( $text =~ m/(?$modifiers)$pattern/ ) {
    print "it matches\n";
}

    [download]
    That is a facet of "Cloistered Pattern Modifiers", as covered on p186 of the Camel Book(3ed.).

    After Compline,
    Zaxo

[reply]
[d/l]
      I don't know how I missed that section. I swear I paged through that chapter several times looking for the answer. I it is a small section I guess... Thanks again.
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