There is a section in perlfunc that explains the file test functions:

                   -e  File exists.
                   -z  File has zero size (is empty).
                   -s  File has nonzero size (returns size in bytes).

                   -f  File is a plain file.
                   -d  File is a directory.

                   -T  File is an ASCII text file.
                   -B  File is a "binary" file (opposite of -T).
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You can use any of these to test for the presence of a file, depending on your exact requirements. For example:

if (-f $my_file)
{
     print "Thanks for not deleting my config file $my_file\n";
}
if (-B $my_file || -z $my_file)
{
     print "I'll bet you think you're funny.\n";
}
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They look odd, I know, functions that start with dashes are a teeny bit unusual, but then again, regular expressions are far stranger.