Stat::lsMode(3) format file modes like the command does


use Stat::lsMode;
$mode = (stat $file)[2];
$permissions = format_mode($mode);
# $permissions is now something like `drwxr-xr-x'
$permissions = file_mode($file); # Same as above
$permissions = format_perms(0644); # Produces just 'rw-r--r--'
$permissions = format_perms(644); # This generates a warning message:
# mode 644 is very surprising. Perhaps you meant 0644...
Stat::lsMode->novice(0); # Disable warning messages


"Stat::lsMode" generates mode and permission strings that look like the ones generated by the Unix "ls -l" command. For example, a regular file that is readable by everyone and writable only by its owner has the mode string "-rw-r--r--". "Stat::lsMode" will either examine the file and produce the right mode string for you, or you can pass it the mode that you get back from Perl's "stat" call.


Given a mode number (such as the third element of the list returned by "stat"), return the appopriate ten-character mode string as it would have been generated by "ls -l". For example, consider a directory that is readable and searchable by everyone, and also writable by its owner. Such a directory will have mode 040755. When passed this value, "format_mode" will return the string "drwxr-xr-x".

If "format_mode" is passed a permission number like 0755, it will return a nine-character string insted, with no leading character to say what the file type is. For example, "format_mode(0755)" will return just "rwxr-xr-x", without the leading "d".


Given a filename, do "lstat" on the file to determine the mode, and return the mode, formatted as above.

Novice Operation Mode

A common mistake when dealing with permission modes is to use 644 where you meant to use 0644. Every permission has a numeric representation, but the representation only makes sense when you write the number in octal. The decimal number 644 corresponds to a permission setting, but not the one you think. If you write it in octal you get 01204, which corresponds to the unlikely permissions "-w----r-T", not to "rw-r--r--".

The appearance of the bizarre permission "-w----r-T" in a program is almost a sure sign that someone used 644 when they meant to use 0644. By default, this module will detect the use of such unlikely permissions and issue a warning if you try to format them. To disable these warnings, use

 Stat::lsMode->novice(0);   # disable novice mode
 Stat::lsMode->novice(1);   # enable novice mode again

The surprising permissions that are diagnosed by this mode are:

        111 => --xr-xrwx
        400 => rw--w----
        440 => rw-rwx---
        444 => rw-rwxr--
        551 => ---r--rwt
        600 => --x-wx--T
        640 => -w------T
        644 => -w----r-T
        660 => -w--w-r-T
        664 => -w--wx--T
        666 => -w--wx-wT
        700 => -w-rwxr-T
        711 => -wx---rwt
        750 => -wxr-xrwT
        751 => -wxr-xrwt
        751 => -wxr-xrwt
        755 => -wxrw--wt
        770 => r------wT
        771 => r------wt
        775 => r-----rwt
        777 => r----x--t

Of these, only 400 is remotely plausible.


As far as I know, the precise definition of the mode bits is portable between varieties of Unix. The module should, however, examine "stat.h" or use some other method to find out if there are any local variations, because Unix being Unix, someone somewhere probably does it differently.

Maybe it "file_mode" should have an option that says that if the file is a symlink, to format the mode of the pointed to file instead of the mode of the link itself, the way "ls -Ll" does.


Mark-Jason Dominus ("[email protected]").