I recall being surprised when I found out that vi was writing a new file with the same name rather than overwriting the existing contents of the file. But testing today shows vi overwriting existing contents. I think this may have changed when truncate became a standard function (or my memory may just be confused, especially since I did a lot of VMS before that).

I'd be very surprised if any of these were false:

• Perl leaves the file open until it is done parsing
• Perl leaves the file open for the duration of the run if there is a __END__ or __DATA__ token in it
• ACME::Bleach works even if your script has an __END__ or __DATA__ token
• Therefore, ACME::Bleach doesn't rely on Perl having closed the script before it modifies it

But this all got me curious.

I checked Bleach.pm and find that it does overwrite the existing script contents (which is what I expected). Perl having the script file open doesn't prevent this from happening.

Win32 is one of the few places where just having the script open would prevent you from deleting it. This makes it convenient for testing this. For example, this script: unlink($0) or warn $!,$/,$^E,$/; successfully deletes itself under Win32 while these two:

unlink($0) or warn $!,$/,$^E,$/;
__END__
[download]

and BEGIN { unlink($0) or warn $!,$/,$^E,$/ } both fail with

Permission denied
The process cannot access the file because it is being used by another
+ process
[download]

So note that your own process can qualify as "another process" as far as this error is concerned. It really should say "via another file handle".

So Perl has the script open while it is parsing it but closes it after that unless you have a __DATA__ or __END__ token. So updating the script while it is running would only cause a problem if you did it while the script was still being parsed or if the script had __DATA__/__END__.

So the script should also be able to delete itself (unless if has __END__/__DATA__ and you haven't closed DATA yet) even under Win32. However, the script probably won't be able to delete the directory that it is in under Win32. If any process is currently chdired to a directory, then you aren't allowed to delete that directory under Win32. (Under Unix, you should be able to delete the script and the directory no matter who has them open.) So you might have to chdir("..") under Win32 and even that might not be enough.

Then again, under Win32 you can also use Win32API::File to request that files/directories that are currently in use be deleted during the next reboot.

Finally, the reason that you can't delete the Perl script while Perl still has it open is because the C run-time library under Win32 defaults to specifying sharing of "rw" and not "rwd". I wish they had opted for "rwd", but my time machine is still broken.

When you open a file in Win32, you specify what type of sharing you would like. Many Win32 programs that don't use the C run-time library's I/O layer specify 0 for the sharing (probably as much because they didn't bother to think about what type of sharing they should be allowing as for any logical reason) so that you can't even look at the file contents while the programming is running. This sucks.

But that is plenty of rambling for now...

        - tye (but my friends call me "Tye")

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