Regexp variable substitution problem in match

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

Good day Monks. I am trying to detect duplicate rows in an array by looking at one element, which is a string. The relevant bit of code is:

if ($items[$i][3] =~ /\b$lastitem[3]\b/) {
     print "DUPLICATE\n";
     $dupcount++;
}
[download]

Problem is, if the match variable contains a regexp special character, like $, it doesn't match. I need to get it to interpret the variable-substituted string literally.

Some kind monks helped me out with a similar problem on the replace side of a substitute statement in this thread, but I can't seem to make the same technique work in the above case. Anyone know how I can solve this problem?

Many thanks

Steve

Comment on Regexp variable substitution problem in match Download Code

Replies are listed 'Best First'.
Re: Regexp variable substitution problem in match by saintmike (Vicar) on Aug 28, 2005 at 01:15 UTC
To make sure that any regex meta characters in `$lastitem[3]` are interpreted literally, surround the scalar by `\Q...\E`: `/\b\Q$lastitem[3]\E\b/` will do the trick, just like running quotemeta on the scalar before using it in a regex.	[reply] [d/l] [select]
Re: Regexp variable substitution problem in match by polettix (Vicar) on Aug 28, 2005 at 01:22 UTC
#!/usr/bin/perl use strict; use warnings; my @against = qw( hi $hi @hi %hi ); foreach my $outer (@against) { foreach (@against) { my $inner = quotemeta; print "[$outer] against [$inner]: "; if ($outer =~ /$inner/) { print "MATCHES\n"; } else { print "NO WAY\n"; } } } __END__ [hi] against [hi]: MATCHES [hi] against [\$hi]: NO WAY [hi] against [\@hi]: NO WAY [hi] against [\%hi]: NO WAY [$hi] against [hi]: MATCHES [$hi] against [\$hi]: MATCHES [$hi] against [\@hi]: NO WAY [$hi] against [\%hi]: NO WAY [@hi] against [hi]: MATCHES [@hi] against [\$hi]: NO WAY [@hi] against [\@hi]: MATCHES [@hi] against [\%hi]: NO WAY [%hi] against [hi]: MATCHES [%hi] against [\$hi]: NO WAY [%hi] against [\@hi]: NO WAY [%hi] against [\%hi]: MATCHES [download] Flavio perl -ple'$_=reverse' <<<ti.xittelop@oivalf Don't fool yourself.	[reply] [d/l]