Your need to work around whitespace is a Perl speciality. This looks like a C programmer's way to attempt the search; free your mind and embrace the Perl way:

Instead of index, use grep. The \s characters will accept any kind of whitespace, be it space character or tab, etc. This is the change I'd recommend:

OLD:  $substr = " 1 ";
NEW:  $substr = '1';
      my $regex = quotemeta $substr;

OLD:  if (index($key, $substr) != -1) {print "\nExist";}
NEW:  if (grep /\s$regex\s/, " $key ") {print "\nExist";}
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Update: In order to ensure a leading or trailing '1' is captured, the grep was modified to include forced whitespace around $key.