When accepting command-line arguments that specify both an input file and an output file, be aware that eventually someone using your program will specify the same filename for both input and output. If your code looks like this:

# Standard open for input, open for output code
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then the result is going to be a blank output file! (or whatever it is your program produces given a blank input file). This isn't very friendly to the user. Slightly more userfriendly is to check for this condition in your code:

if ($infile eq $outfile)
{
  die "Same filename given for both input and output!";
}
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This protects against a user who accidentally uses the same filename for input and output, but doesn't protect against filenames which are different strings but name the same file (for example, "foo" and "./foo", or "foo" and "bar", if "bar" is a symbolic link to "foo")

However, it may be the case that the occasional user actually does want the output file to replace the input file, much as perl's own -i option does. Certainly, if possible, we should allow this since we want our programs to be useful to the user. In this case: (... and here continue on with the unlink trick, etc.)

@/=map{[/./g]}qw/.h_nJ Xapou cets krht ele_ r_ra/;
map{y/X_/\n /;print}map{pop@$_}@/for@/
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