maybe what you want is

$agent =~ m/[A-Za-z]*/;
[download]

which will match a string of characters (uppercase or lowercase) or

$agent =~ m/PerlBeginner(Perl)?/;
[download]

Which will match the strings "PerlBeginner" and "PerlBeginnerPerl".

All of this is documented in the perlre perldoc.

1. dude, what does mine say?
2. "sweet", what about mine?
3. "dude", what does mine say?
4. GOTO 2