And that is just what your script is already doing. I changed your script slightly to make it a bit more obvious:

#!/usr/bin/perl
use warnings;

my $gotit = "";
until ("" ne $gotit) {
$gotit = <DATA>; # Look for the pattern "abcd" in the incoming data
chomp $gotit;
if($gotit){last;} # to exit the loop after the pattern detection

print("Pattern is not detected\n"); # print the message till pattern i
+s detected.
}

print "action after the loop\n";


__DATA__



bingo
[download]

This prints:

Pattern is not detected
Pattern is not detected
Pattern is not detected
action after the loop
[download]