Is there a Perl function to turn a string into a regexp to use that string as pattern?

Question

I have trouble using Perl grep() with a string that may contain chars that are interpreted as regular expressions quantifiers.

I got the following error when the grep pattern is "g++" because the '+' symbols are interpreted as quantifiers. Here is the output of for program that follows:

1..3
ok 1 - grep, pattern not found
ok 2 - grep, pattern found

Nested quantifiers in regex; marked by <-- HERE
in m/g++ <-- HERE / at escape_regexp_quantifier.pl line 8.

Is there a modifier I could use to indicate to grep that the quantifiers shall be ignored, or is there a function that would escape the quantifiers ?

#! /usr/bin/perl 

sub test_grep($)
{
    my $filter = shift;
    my @output = ("-r-xr-xr-x   3 root     bin       122260 Jan 23  2005 gcc",
                  "-r-xr-xr-x   4 root     bin       124844 Jan 23  2005 g++");
    return grep (!/$filter/, @output);
}

use Test::Simple tests => 2;

ok(test_grep("foo"), "grep, pattern not found");
ok(test_grep("gcc"), "grep, pattern found");
ok(test_grep("g++"), "grep, pattern found");

PS: in addition to the answer question above, I welcome any feedback on Perl usage in the above as I'm still learning. Thanks

Answer 1

The standard way is to use the \Q escape indicator before your variable, to tell Perl not to parse the contents as a regular expression:

return grep (!/\Q$filter/, @output);

Altering that line in your code yields:

1..3
ok 1 - grep, pattern not found
ok 2 - grep, pattern found
ok 3 - grep, pattern found

Answer 2

I think you are looking for quotemeta