If you had used Data::Dumper to look at @dir_files like I suggested, you'd see strings such as "-rw-rw---- 1 xupromgr xupromgr           10 Feb 27 14:08 auditsample.txt", which won't match the regex /^audit/. Try using the command $ftp->ls instead of $ftp->dir to list files, this should give you a listing consisting of file names only.

You should always Use strict and warnings, and see also the Basic debugging checklist.