Re: Unlinking a file when the file doesnt exist

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Re^2: Unlinking a file when the file doesnt exist by cdarke (Prior) on Mar 22, 2011 at 17:19 UTC
A good reason for using this solution is that, in theory at least, you could have a possible race condition with your code. Between check for the existence of the file (-e) and deleting the file another process could have deleted it or even opened it.	[reply]
Re^3: Unlinking a file when the file doesnt exist by ikegami (Patriarch) on Mar 22, 2011 at 19:05 UTC
It's not a race condition. It doesn't matter when the file was created or haw many times it was created. The file should be gone and it's not.	[reply]
Re^2: Unlinking a file when the file doesnt exist by ikegami (Patriarch) on Mar 22, 2011 at 19:07 UTC
Unfortunately, `$!` is garbage in that example. It would only be meaningful if `stat` (via `-e`) failed. One definitely cannot count on it having any info about an `unlink` error. I recommend `for my $file (qw(files.txt data.txt)) { unlink($file) or $!{ENOENT} or die("Unable to unlink '$file': $!"); }` [download] Or if one wants to clean up as many files as possible even if some can't be deleted, `my $success = 1; for my $file (qw(files.txt data.txt)) { if (!unlink($file) && !$!{ENOENT}) { warn("Unable to unlink '$file': $!"); $success = 0; } } die("Unable to cleanup") if !$success;` [download]	[reply] [d/l] [select]
Re^3: Unlinking a file when the file doesnt exist by moritz (Cardinal) on Mar 22, 2011 at 21:19 UTC
Unfortunately, $! is garbage in that example. It contained the right value when I tried it. Is that platform (or perl version) dependent? Perl 6 - second systems done right	[reply]
Re^4: Unlinking a file when the file doesnt exist by ikegami (Patriarch) on Mar 22, 2011 at 21:31 UTC
It may have the right value if you're lucky. `stat` is free to change it, and you can reach the `die` even if `unlink` was successful.	[reply] [d/l] [select]
Re^3: Unlinking a file when the file doesnt exist by Gulliver (Monk) on Mar 23, 2011 at 15:12 UTC
Unfortunately, $! is garbage in that example. From unlink: Deletes a list of files. On success, it returns the number of files it successfully deleted. On failure, it returns false and sets $! (errno): One of the examples at the perldoc page for unlink shows using $! with warn() in a foreach loop. Why shouldn't $! be used in this case?	[reply]
Re^4: Unlinking a file when the file doesnt exist by ikegami (Patriarch) on Mar 23, 2011 at 15:47 UTC
I didn't say anything that contradicts that. It's perfectly fine to use `$!` immediately after `unlink` returns an error as I showed in the very post you quoted. In moritz's code, `$!` isn't being used immediately after `unlink` returns an error. In decreasing likeliness of occurrence, It's sometimes used after `stat` (`-e`) successfully returns false. (Can change `$!`.) It's sometimes used after `stat` (`-e`) returns an error. (Always sets `$!`.) It's sometimes used after `unlink` returns success. (!!!)	[reply] [d/l] [select]
Re^2: Unlinking a file when the file doesnt exist by Gulliver (Monk) on Mar 22, 2011 at 18:15 UTC
What if the file is actually a directory? I have never tried it but the documentation for unlink gives some warnings. How about: `for my $file (qw(files.txt data.txt)) { unlink $file if -f $file; die "Unable to unlink '$file': $!" if -e $file; }` [download] Update: If the file tests are different then it would die after not attempting to delete a directory and $! would not be set. In that case -f is false and -e is true. If I make them the same that won't happen. `for my $file (qw(files.txt data.txt)) { unlink $file if -f $file; die "Unable to unlink '$file': $!" if -f $file; }` [download] Better yet; do an unlink or warn. `for my $file (qw(files.txt data.txt)) { if ( -f $file) { unlink $file or warn "Unable to unlink '$file': $!"; } }` [download]	[reply] [d/l] [select]