if statement - Perl If-Elsif-Else always going to else -

i have block of code in larger program suppose take letter (a...d) , convert number (0...3). reason jumps down else. here code:

        $aa = shift @filearray;          chomp($q);         chomp($a1);         chomp($a2);         chomp($a3);         chomp($a4);         chomp($aa);         print "1:$aa\n";      #convert answer number      $ab = 0;         if ($aa eq "a")         {             $ab = 0;         }          elsif ($aa eq "b")         {             $ab = 1;         }          elsif ($aa eq "c")         {             $ab = 2;         }          else {             $ab = 3;         }         print "2:$ab\n\n"; 

the output along lines of

    1:b     2:3      1:a     2:3      1:d     2:3      1:c     2:3      1:d     2:3      1:b     2:3      1:b     2:3      1:a     2:3      1:d     2:3 

now realize @ point subtract 65 ascii value, still want know...what happening?

maybe $aa contains invisible characters (whitespace, carriage return). verify $aa contains think does: single character. 1 way check this:

length($aa) == 1 

more advanced , more informative checks include:

use data::dumper; local $data::dumper::useqq = 1; print dumper($aa); 

and

print join ' ', map { ord } split //, $aa; 

and

printf '%v02x\n', $aa; 

the last check displays ordinal values every character in $aa.