Be aware of false strings that match.

use List::Util 'first';

my $var = '0';

if (first { $_ eq $var } $var) {
  print "Found.\n";
}
else {
  print "Not found.\n";
}

__END__
Not found.
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You could solve this by using defined in this particular case, but it's not a general solution. As Herkum says, any from List::MoreUtils is a better alternative in the general case.

lodin