Howdy doubleqq, welcome back to the Monastery!

This is my code that works but runs slow:

Are you sure that's your actual code, your working code? I'm asking because of this:

print RESULT “Company"."\t”.”Name"."\t”.”Title"."\n";
[download]

and this:

if (($match[0] =~/\Q$sTab[1]\E/) and (define $match[1])){
[download]

“ and ” aren't valid quoting characters in Perl, and define isn't a (built-in) function: you most likely meant defined there, but the uncaught typo makes me wonder.

That said, here's two tips:

• Don't do things in loops that you can do outside loops. In particular, pre-process your data as much as possible.
• Use data structures that are a natural fit for what you're trying to accomplish.

In your code, you're not just needlessly reprocessing your list of names and titles, you're doing so for every single last line read from your $longList. Don't do that; preprocess it into an efficient data structure, e.g. a hash, and do so outside the main loop. Better yet, have whatever generates this list generate a hash in the first place, if that is an option.

For example, take the following:

#!/usr/bin/perl

use strict;
use warnings;
use feature qw/say/;

# I'm assuming you can't control how @flab is populated.
my @flab;
push @flab, "name_$_\ttitle_$_" for (1..200);

# turn @flab into a hash
my %titles = ();
foreach (@flab) {
    my ($name, $title) = split /\t/;
    $titles{$name} = $title;
}

open my $LONG_LIST, "<", "longlist.txt" or die "Cannot open file: $!";

say "Company\tName\tTitle";
while (<$LONG_LIST>) {
    chomp;
    my ($company, $name) = split /\t/;;

    say "$company\t$name\t$titles{$name}" if($titles{$name});
}
[download]

To test this, I generated a longlist.txt file as follows:

$ for i in `seq 1 72000`; do echo -e company_${i}\\tname_${i} >>longli
+st.txt ; done
[download]

The above script then runs in 0.122s (wallclock time) on my system, compared to about 13s for the version you posted above, a speedup of a factor of more than 100. With bigger @flabs, you'll see even more of a speedup.

Other notes:

• Your script as posted will not work correctly when you've got names that are contained in other names. For instance, if you've got both Fred Larry Flintstone and Larry Flint in your @flab, and your $longList contains an entry for the latter, you'll get output for both, which I assume is not what you want.
• Your output columns won't line up if your company names/names/titles get too long; if that's undesired, you could use Text::Table or so to get nicer output with a minimum of effort.

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