First, any white space or punctuation will be considered to be numeric - I somehow don't think that is what you want. This can be fixed by adding an elsif clause with a condition of $string =~ /^\d+$/. Of course, then you have to decide if white space and punctuation are valid inputs are not.

Second, consider the strings "a2" and "2a" - both will be considered Alphabet but your code. There is at least one character in each string thus the match succeeds. You want to anchor the match, something like $string =~ /^[a-zA-Z]+$/.

Third, are you sure that you want to use $a as a variable name. It has the same name as the built in sort variable and you did make it a my variable but to save yourself possible future bugs I would recommend against using $a (and $b) as temporary variables names.

The tests would probably look something like

if($string =~ /^[a-zA-Z]$/) # can also be written as /^[a-z]$/i
{
   print "Alphabet\n";
}
elsif($string =~ /^\d+$/)
{
   print "Number\n";
}
else
{
   print "Other\n";
}
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Edit: chipmunk 2001-03-22