Re: Re: Re: unlink Question

Well, actually, it does (or if you wanna be anal, it depends). Please don't spread misinformation

from perldoc -f

unlink LIST
unlink  Deletes a list of files. Returns the number of files
        successfully deleted.

            $cnt = unlink 'a', 'b', 'c';
            unlink @goners;
            unlink <*.bak>;

        Note: "unlink" will not delete directories unless you are
        superuser and the -U flag is supplied to Perl. Even if these
        conditions are met, be warned that unlinking a directory can
        inflict damage on your filesystem. Use "rmdir" instead.

        If LIST is omitted, uses $_.

from perlport

Don't unlink or rename an open file.

Don't assume that a single unlink completely gets rid of the file: some filesystems (most notably the ones in VMS) have versioned filesystems, and unlink() removes only the most recent one (it doesn't remove all the versions because by default the native tools on those platforms remove just the most recent version, too). The portable idiom to remove all the versions of a file is

    1 while unlink "file";

This will terminate if the file is undeleteable for some reason (protected, not there, and so on).

Some operating systems don't have links at all.

Comment on Re: Re: Re: unlink Question

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Re: Re: Re: Re: unlink Question by sauoq (Abbot) on Nov 11, 2003 at 20:08 UTC
Please don't spread misinformation. I wasn't. Well, actually, it does* (or if you wanna be anal, it depends).* Right. It depends. In other words, `unlink()` does not delete files; it does something else which might result in files being deleted. I really don't care what `perldoc -f unlink` says because, in this case the docs are not, as you put it, "anal." Their imprecision is forgivable because it is a messy topic with multiple exceptions depending on operating system and filesystem features. On Unix, Perl's native platform, unlinking generally removes a directory entry, or "link". Hence the name of the function. Although many files have only a single directory entry, that's not at all guaranteed. In that case, if you call `unlink()` and pass just one of the file's directory entries, the file itself will not be removed even if `unlink()` successfully removes the link and returns 1. Also, on Unix, unlinking an open file works just fine. I've even seen it used on purpose. Nevermind what perlport says; not everyone cares about writing portable Perl. Versioned filesystems, as you yourself point out, are another example of how `unlink()` may not delete a file. There is a variable, `UNLINK_ALL_VERSIONS`, however, which can be defined at compile time to make perl on VMS behave similarly to perl on Unix. Some operating systems don't have links at all. And, on those crippled platforms, the overly simplistic explanation given in `perldoc -f unlink` is sufficient. -sauoq "My two cents aren't worth a dime.";	[reply]

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Re: Re: Re: Re: unlink Question
by sauoq (Abbot) on Nov 11, 2003 at 20:08 UTC

Please don't spread misinformation.

I wasn't.

Well, actually, it does (or if you wanna be anal, it depends).

Right. It depends. In other words, unlink() does not delete files; it does something else which might result in files being deleted. I really don't care what perldoc -f unlink says because, in this case the docs are not, as you put it, "anal." Their imprecision is forgivable because it is a messy topic with multiple exceptions depending on operating system and filesystem features.

On Unix, Perl's native platform, unlinking generally removes a directory entry, or "link". Hence the name of the function. Although many files have only a single directory entry, that's not at all guaranteed. In that case, if you call unlink() and pass just one of the file's directory entries, the file itself will not be removed even if unlink() successfully removes the link and returns 1.

Also, on Unix, unlinking an open file works just fine. I've even seen it used on purpose. Nevermind what perlport says; not everyone cares about writing portable Perl.

Versioned filesystems, as you yourself point out, are another example of how unlink() may not delete a file. There is a variable, UNLINK_ALL_VERSIONS, however, which can be defined at compile time to make perl on VMS behave similarly to perl on Unix.

Some operating systems don't have links at all.

And, on those crippled platforms, the overly simplistic explanation given in perldoc -f unlink is sufficient.

-sauoq
"My two cents aren't worth a dime.";

[reply]