The previous posts have pointed you in the right direction with regard to your question and file test operators. I would only add some additional information about a lesser known module included with the core Perl distribution which may also be of use if testing for the existence of a large number of files.

The File::CheckTree module can be used to perform file tests on a large number of files within a directory tree. For example, from the documentation for this module:

use File::CheckTree;

$warnings += validate( q{
    /vmunix                 -e || die
    /boot                   -e || die
    /bin                    cd
        csh                 -ex
        csh                 !-ug
        sh                  -ex
        sh                  !-ug
    /usr                    -d || warn "What happened to $file?\n"
});
[download]

The real power of this module however lies in the ability to perform a great number of file tests, moreso than existence (-e) checks, on a large group of files as the example above demonstrates.

 

perl -e 'print+unpack("N",pack("B32","00000000000000000000000111001110")),"\n"'