for (qw(a X b)) {
    my $id = $1
      if /(a)/ or /(b)/;

   print qq{'$_' -> '$id'\n};

}

##</code><code>##

C:/Perl_524/bin\perl.exe -w d:/exp/pm_or_regex.pl 
Use of uninitialized value $id in concatenation (.) or string at d:/exp/pm_or_regex.pl line 5.
'a' -> 'a'
'X' -> ''
'b' -> 'b'