This solves both your problems (if I interpret you correctly):

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