Re: Maybe a bug in chmod (and others) making command recursive

[Jon Stanley]

On Tue, Nov 18, 2014 at 12:02 PM, operations
<address@hidden> wrote:
> I'm uncertain whether this is a chmod bug or not, as using ./* instead of * 
> works as expected - it may also be expected. But on the other hand, having 
> security-related commands like chmod doing different things depending on the 
> files in the current directory seems to me also not to be the correct 
> behaviour. BTW This above also applies to rm, which deletes all the files 
> recursively if there is a file called -r in the directory (at least there is 
> a sentence about files with leading "-", even no information that they make 
> rm recursive ...)

This isn't a bug in chmod, or anything else really, but rather the
expected behavior of shell globbing. The parsing of the '*' on the
command line is done by your shell, prior to the invocation of chmod.
Therefore, chmod has no way to tell whether you typed -R, or it was
expanded by the shell.

As an example:

$ ls -lR
.:
total 4
-rwxr-xr-x. 1 jstanley jstanley    0 Nov 18 12:54 -R
drwxrwxr-x. 2 jstanley jstanley 4096 Nov 18 12:58 some-dir
-rwxrwxrwx. 1 jstanley jstanley    0 Nov 18 12:54 some-file

./some-dir:
total 0
-rw-rw-rw-. 1 jstanley jstanley 0 Nov 18 12:58 some-file
$ echo *
-R some-dir some-file

As you can see from the 'echo *', the shell expanded it into '-R
some-dir some-file'. Therefore, doing 'chmod *' is literally
equivalent to typing 'chmod -R some-dir some-file' on the command
line.

Fortunately, chmod and other GNU utilities have a way to protect
against this shell expansion - the '--' option, which indicates to
stop processing further options on the command line and the remainder
of the command line is arguments. For example, from the previous
directory:

$ chmod -- 755 *
$ ls -lR
.:
total 4
-rwxr-xr-x. 1 jstanley jstanley    0 Nov 18 12:54 -R
drwxr-xr-x. 2 jstanley jstanley 4096 Nov 18 12:58 some-dir
-rwxr-xr-x. 1 jstanley jstanley    0 Nov 18 12:54 some-file

./some-dir:
total 0
-rw-rw-rw-. 1 jstanley jstanley 0 Nov 18 12:58 some-file

Notice how my 'some-dir/some-file' retains the mode that I originally had, 0666.

Hope that helps!
-Jon