regex special chars in interpolated variables

[domster]

Hi, I'm hoping someone out there can save me the bother of searching through the manuals. Is there any way of telling Perl not to treat reserved characters (+, * etc) as special when they occur in interpolateed variables? For example, I had an array of various codes, some of which began with a +, and I was running through the array, looking for each in a string:

while ($i < $#codearray) {
$code = $codearray[$i];
if ($stringtosearch =~ s/^(\s*)$gramcode//) {
...
last;
}
$i++;
}

I couldn't work out for ages why the codes beginning with + weren't getting found, then I realised Perl was treating them as sepcial characters. I converted the + to \+ in the codes, but is there a better way of doing it? Thanks,

Dom

 

[Nebbish]

Yep! I actually asked this very same question a few weeks ago. Use /Q and /E within the regexp; it treats $variables as variables, but treats any regexp syntax within those strings literally:

my $string = 'I got an A+ in school today!';
if(/\Q$string\E/) {
  print "String matches.";
} else {
  print "String doesn't match.";
}

HTH,

Nick

 

[toolkit]

Yep, use \Q and \E. See man perlre for more.
Example:

#!/usr/bin/perl -w
my $pat = ".*a+";
my @strings = qw( .*a+ fffaa );
## wrong
foreach $string (@strings) {
    print "$string matches $pat\n" if $string =~ m/$pat/;
}
## right
foreach $string (@strings) {
    print "$string matches $pat\n" if $string =~ m/\Q$pat\E/;
}

Cheers, Neil

 

[domster]

\Q and \E - of course, silly me! Thanks both for the very fast response.

Dom