It's not clear to me exactly what you're trying to do, but I wonder if perhaps you need an  | "ordered alternation" operator:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $p1 = qr{ Foo }xms;
 my $p2 = qr{ Bar }xms;
 my $p3 = qr{ Zot }xms;
 ;;
 my $str = 'Bar';
 ;;
 if (my ($m) = $str =~ m{ \A ($p1 | $p2 | $p3) \z }xms) {
   print qq{matches: has '$m'};
   }
"
matches: has 'Bar'
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Update:

my ($m1) = $output =~ /^(pattern1)$/ or my ($m1) = $output =~ /^(pattern2)$/ or my ($m1) = $output =~ /(pattern3)/

BTW: An expression like the one quoted above, with multiple masking variables (i.e., variables having the same name) defined in the same scope is never a good idea, and Perl would have told you about this ugly situation had you enabled warnings with a  use warnings; statement at the top of your program. Especially for those just starting with Perl, always  use warnings; and  use strict; at the start of your code.