foreach my $file (grep { !-e } @files) # The grep returns all the elements of the array
                                       # for which the sub ( { !-e } ) returns true, which it
                                       # will only if $_ (the array element being tested) does not
                                       # exist.  If you want it to exist and be a
                                       # regular file (as opposed to a directory, FIFO, etc.)
                                       # use -f.
{
    local *FH;                         # To make sure we don't clobber FH.
    open FH, ">>$file";                # In case the file got created
                                       # in the meantime, we use the append operator to avoid
                                       # clobbering data.
    close FH;                          # And then we close it.
}