my @files_to_do;
if ( @ARGV and -f $ARGV[0] )
    @files_to_do = @ARGV;
}
else {
    print "Enter file name(s), separated by space and/or newline:\n" if ( -t );
    while (<STDIN>) {
        chomp;
        push @files_to_do, split //;
    }
}
die "Nothing to do\n" unless @files_to_do;

# now do something that loops over @files_to_do...


##</code><code>##

ls | my_backup.pl
find some_path -name '*.foo' | my_backup.pl