Capturing groups in a variable regexp in Perl

Question

I have a bunch of matches that I need to make, and they all use the same code, except for the name of the file to read from, and the regexp itself. Therefore, I want to turn the match into a procedure that just accepts the filename and regexp as a string. When I use the variable to try to match, though, the special capture variables stopped being set.

$line =~ /(\d+)\s(\d+)\s/;

That code sets $1 and $2 correctly, but the following leaves them undefined:

$regexp = "/(\d+)\s(\d+)\s/";
$line =~ /$regexp/;

Any ideas how I can get around this?

Thanks, Jared

Answer 1

Use qr instead of quotes:

$regexp = qr/(\d+)\s(\d+)\s/;
$line =~ /$regexp/;

Answer 2

Quote your string using the perl regex quote-like operator qr

$regexp = qr/(\d+)\s(\d+)\s/;

This operator quotes (and possibly compiles) its STRING as a regular expression.

See the perldoc page for more info: http://perldoc.perl.org/functions/qr.html

Answer 3

Quote your regex string usin qr :

my $regex = qr/(\d+)\s(\d+)\s/;
my $file =q!/path/to/file!;
foo($file, $regex);

then in the sub :

sub foo {
my $file = shift;
my $regex = shift;

open my $fh, '<', $file or die "can't open '$file' for reading: $!";
while (my $line=<$fh>) {
    if ($line =~ $regex) {
        # do stuff
    }
}