Something like this?

use strict;
use warnings;
use autodie qw/:all/;

open my $outfile, '>', 'filename.txt';

while (<>) {
    if ( m#-/(\w+)\?srt=# ) {
        print $outfile $1, "\n";
    }
}
close $outfile;
[download]

Update: Rats, the preceding example assumes one match per line. That's not a certainty though. How about this:

use strict;
use warnings;
use autodie qw/:all/;
open my $outfile, '>', 'filename.txt';
while ( <> ) {
    while( m#-/(\w+)\?srt=#g ) {
        print $outfile $1, "\n";
    }
}
close $outfile;
[download]

There's another nifty way too. If you don't really care about newlines as record separators, why not call the '?srt=' your record separator instead? In that case, it would look like this:

use strict;
use warnings;
use autodie qw/:all/;

open my $outfile, '>', 'filename.txt';
{
    $local $/ = '?srt=';
    while( <> ) {
        chomp;
        if( m#-/(\w+)$# ) {
            print $outfile $1, "\n";
        }
    }
}
close $outfile;
[download]