Question

I think this question is repeated, but searching wasn’t helpful for me.

my $pattern = "javascript:window.open\('([^']+)'\);";
$mech->content =~ m/($pattern)/;
print $1;

I want to have an external $pattern in the regular expression. How can I do this? The current one returns:

Use of uninitialized value $1 in print at main.pm line 20.

Answer 1

$1 was empty, so the match did not succeed. I’ll make up a constant string in my example of which I know that it will match the pattern.

Declare your regular expression with qr, not as a simple string. Also, you’re capturing twice, once in $pattern for the open call’s parentheses, once in the m operator for the whole thing, therefore you get two results. Instead of $1, $2 etc. I prefer to assign the results to an array.

my $pattern = qr"javascript:window.open\('([^']+)'\);";
my $content = "javascript:window.open('something');";
my @results = $content =~ m/($pattern)/;
# expression return array
# (
#     q{javascript:window.open('something');'},
#     'something'
# )