#!/usr/bin/perl -w

print "get some string: ";
($string = <STDIN>);
#note: chomp not necessary, $ should count \n as
#end of string. should work with or without chomp.

$string =~ m/\/([[:alnum:]]+)_.*\.(.+)$/;
print "dollar 1: $1\n";
$type = $2;
print "type: $type\n";

#something weird here....
$string =~ m/(.+)\.BBB$/;
   #get some string: /xxxx/yyyy/ZZZ_xxxx.CCC
   #dollar 1: ZZZ
   #type: CCC
   #dollar 1:ZZZ
   
print "match failed\n" unless $string =~ m/(.+)\.BBB$/;   
   
#$string =~ m/(.+)\.${type}$/; #ok
#$string =~ m/(.+)\.$type$/;   #ok also

print "dollar 1:$1\n";

exit 0;
__END__

This is with the match failed code:
C:\TEMP>regextest.pl
get some string: /xxxx/yyyy/ZZZ_xxxx.CCC
dollar 1: ZZZ
type: CCC
match failed
dollar 1:ZZZ

This is from: 
#$string =~ m/(.+)\.${type}$/; #ok
#$string =~ m/(.+)\.$type$/;   #ok also
C:\TEMP>regextest.pl 
get some string: /xxxx/yyyy/ZZZ_xxxx.CCC
dollar 1: ZZZ
type: CCC
dollar 1:/xxxx/yyyy/ZZZ_xxxx

C:\TEMP>perl -v
This is perl, v5.10.0 built for MSWin32-x86-multi-thread
(with 5 registered patches, see perl -V for more detail)