john@perl:~$ perl -le'
my $file_name = q[];
$tst = q[test\test web\test libb\file.-finaltestfla.jar];

$file_name = $1 if ($tst =~ m/\A\S+\\(.*?\.jar)\z/i);

print $file_name . "\n" . $tst;
'
test web\test libb\file.-finaltestfla.jar
test\test web\test libb\file.-finaltestfla.jar