Регулярки

TF=([0-9]{1,2});

~TF=(\d{1,2})~

use strict;
use warnings;
 
my @cases = qw(TF=22; BT=22; =220;);
for my $str (@cases) {
    my @matches = $str =~ /^TF=(\d{1,2});$/;
    if (@matches) {
        print "Got it: $str -> $matches[0]\n";
    } else {
        print "Nothing to do with: $str\n";
    }
}

/^TF=(\d{1,2});$/

$matches = null;
$returnValue = preg_match('#TF=(?<number>\d\d);#', 'TF=23;', $matches);
if ($returnVaue)
{
     echo $matches['number'];
}

$matches = null;
$returnValue = preg_match_all('#TF=(?<number>\d\d);#', 'TF=23;fF=asasd;TF=12;TF=123;', $matches);
if ($returnVaue)
{
     print_r($matches['number']);
}