Re: creating a regular expression's alternation dynamically?

#!/usr/bin/perl
use strict;
#   create alternation
my @list;
while (<DATA>) {
    chomp;
    push @list, $_;
}
my $regex = '^(' . join('|', @list) . ')$';
my $s = 'huey';
print "regex = $regex\n";
print "match:\t$1\n" if $s =~ m/$regex/;
__DATA__
huey
dewey
louie
[download]

Running the program...

C:\Temp\test>perl test.pl
regex = ^(huey|dewey|louie)$
match:  huey
[download]

Comment on Re: creating a regular expression's alternation dynamically? Select or Download Code

Replies are listed 'Best First'.
Re^2: creating a regular expression's alternation dynamically? by integral (Hermit) on Aug 06, 2004 at 14:39 UTC
In the join, you might want to map `quotemeta` over @list so that any meta-chars (particulary \|) get escaped. Also you have to be careful that none of the strings are prefixes of another string, otherwise you'll find that ordering is significant in an alternation. -- integral, resident of freenode's #perl	[reply] [d/l]
Re^3: creating a regular expression's alternation dynamically? by mifflin (Curate) on Aug 06, 2004 at 17:27 UTC
yep, good point, thanks! `use strict; use warnings; # create alternation my @list; while (<DATA>) { chomp; push @list, $_; } my $regex = '^(' . join('\|', map {quotemeta} @list) . ')$'; my $s = 'huey'; print "regex = $regex\n"; print "match:\t$1\n" if $s =~ m/$regex/; __DATA__ huey de\|wey louie` [download] output is... `# perl test.pl regex = ^(huey\|de\\|wey\|louie)$ match: huey` [download]	[reply] [d/l] [select]