Checking for directory write permissions

sara2005 has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Checking for directory write permissions by ikegami (Patriarch) on Jun 26, 2006 at 18:06 UTC
You can use `-w` on directories. But do you really need to check that? Just check whether `open` fails or not by examing `$!`: `$ perl -le 'open(FILE, ">", "nowrite/newfile") > or die("Unable to create file: $!\n")' Unable to create file: Permission denied` [download] Update: I originally checked if the dir was readable. Fixed.	[reply] [d/l] [select]
Re: Checking for directory write permissions by shmem (Chancellor) on Jun 26, 2006 at 18:21 UTC
Just use `if( not -w $dir) { die "directory $dir not writeable.\n"; }` [download] The test `-w` works for files and directories. See perlfunc, -X (file tests). _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l] [select]
Re^2: Checking for directory write permissions by sara2005 (Scribe) on Jun 26, 2006 at 18:30 UTC
Thanks a lot -w option worked!!	[reply]
Re^3: Checking for directory write permissions by Tanktalus (Canon) on Jun 27, 2006 at 03:34 UTC
Warning. The -w option will give you a misleading postive result in the case where you have permissions, but the partition is mounted read-only (popular for NFS on unix). We actually just wrote a quick function to test writeability by opening a file for write access wherever we were checking, and, if successful, deleting it afterwards. It was the only foolproof way we could come up with of detecting the situation.	[reply]
Re: Checking for directory write permissions by Fletch (Bishop) on Jun 26, 2006 at 18:15 UTC
As an alternate to using -w or stat, just try and write and handle the error. If the open returns failure check if `$! == EACCESS`; if it does then there was a permissions problem (presuming you've done a `use POSIX qw( :errno_h )` of course).	[reply] [d/l] [select]
Re^2: Checking for directory write permissions by ptum (Priest) on Jun 26, 2006 at 20:10 UTC
I think this is a better solution, or at least one that should not be overlooked. Actually trying to write the file can also expose other errors (disk full comes to mind, etc.) which may not be identified by a simple -w (especially at the directory level). No good deed goes unpunished. -- (attributed to) Oscar Wilde	[reply]