No good. "b matches a" doesn't necessarily follow from "a matches b". In fact, when it does, you should be using eq, not a regexp. 

use strict;
use warnings;

my $var_a = '';
my $var_b = 'abc';
my $var_c = '';

if (  $var_a =~ /abcdefgh/
   || $var_b =~ /abcdefgh/
   || $var_c =~ /abcdefgh/
) {
   print("orig: true\n");
} else {
   print("orig: false\n");
}

if ( q{abcdefgh} =~ /(?:$var_a|$var_b|$var_c)/ ) {
   print("johngg: true\n");
} else {
   print("johngg: false\n");
}

[download]
outputs 
orig: false
johngg: true

[download]

In reply to Re^2: howto make a very long IF statment shorter by ikegami
in thread howto make a very long IF statment shorter by jeanluca

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