Try something along the lines of

...
my $match = 0;
for (@line) {
    ...
    if ($_ =~ /$search/i) {
        print ...;
        $match++;
    }
}
if (!match) {
    print "not found";
}
[download]

Read Transient's reply above, he is right. His "found" variable is called $match here. A similar trick is used in this program, where the flag $found_any is used in the same manner, and later it is used to generate the exit code.