That's a perfect example of why you should be reading the directory listing from within Perl (i.e. the opendir/readdir solution), rather than using a non-portable external command.

On the department's server, `ls` is aliased to `ls -F`. The -F option causes ls to add * to executables, / to directories, and @ to symbolic links. Useful when looking at a directory listing from the command prompt; not useful when getting a list of filenames within Perl.