Re: Backticks, $?, and Sudo

Answers:

Sudo should return the exit value of the command that was run.

$ sudo perl -e 'exit 3'
$ echo $?
3
[download]

A better example might be:

$ perl -le '`sudo perl -e "exit 3"`; print $?>>8'
3
[download]

Are you sure that is CHILD_ERROR you are looking at and not ERRNO? The reason I ask is twofold. The first is that $? should be numeric. The second is that I've often seen $! being set to "Illegal Seek" after a successful backtick command. I think it has to do with how perl implements the backticks. (Specifically, I think it attempts to do a seek on the pipe. I have no idea why though.) In any case, it doesn't much matter because $! isn't really applicable unless the return value extracted from $? is -1.
That depends...

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

Comment on Re: Backticks, $?, and Sudo Select or Download Code

Replies are listed 'Best First'.
Re: Re: Backticks, $?, and Sudo by ignatz (Vicar) on Jan 17, 2003 at 18:12 UTC
Thanks for everyone's response. helgi response makes a lot of sense. I keep forgetting that they are magic variables with super powers. I guess that the thing that I find really puzzling is how $! and $? act completely different when sudo is thrown into the mix: $> perl sudotest.pl Password: sudo: /foo/bar/paco: command not found $ sudo /foo/bar/paco ERRNO = CHILD_ERROR = 256 **************************************** Can't exec "/foo/bar/paco": No such file or directory at sudotest.pl l +ine 8. $ /foo/bar/paco ERRNO = No such file or directory CHILD_ERROR = -1 Use of uninitialized value in print at sudotest.pl line 12. ************************************** $ ls -laF ERRNO = Illegal seek CHILD_ERROR = 0 total 138 drwxrwxrwx 5 ignatz paco 1024 Jan 16 15:16 ./ drwxr-xr-x 21 ignatz paco 1536 Jan 16 15:34 ../ drwxrwxrwx 2 ignatz paco 512 Dec 18 15:30 CVS/ -rw-r--r-- 1 ignatz paco 298 Jan 16 14:44 sudotest.pl **************************************** [download] I should have included this in the first place. ()-() \"/ `	[reply] [d/l]
Re: Re: Re: Backticks, $?, and Sudo by sauoq (Abbot) on Jan 17, 2003 at 18:34 UTC
Uhm... $! and $? do not act differently with sudo thrown in the mix. The only real difference is that you are executing a different command (i.e. sudo rather than the command that sudo is executing.) `$> perl sudotest.pl Password: sudo: /foo/bar/paco: command not found $ sudo /foo/bar/paco ERRNO = CHILD_ERROR = 256` [download] In that case, sudo executed just fine and returned a 1 (which is what sudo does when the command it is given can't be executed.) Remember to shift $?. (256 >> 8 == 1) `Can't exec "/foo/bar/paco": No such file or directory at sudotest.pl l +ine 8. $ /foo/bar/paco ERRNO = No such file or directory CHILD_ERROR = -1 Use of uninitialized value in print at sudotest.pl line 12.` [download] Again, normal behavior. Perl can't execute the command given so it sets $? to -1 and returns the reason in $! (as documented.) `$ ls -laF ERRNO = Illegal seek CHILD_ERROR = 0 total 138 drwxrwxrwx 5 ignatz paco 1024 Jan 16 15:16 ./ drwxr-xr-x 21 ignatz paco 1536 Jan 16 15:34 ../ drwxrwxrwx 2 ignatz paco 512 Dec 18 15:30 CVS/ -rw-r--r-- 1 ignatz paco 298 Jan 16 14:44 sudotest.pl` [download] Once again, this behaved as expected. The command executed successfully, so $? contains 0. In this case, $! is not relevant. Keep in mind that $! is only meaningful in association with backticks and system when $? == -1. -sauoq "My two cents aren't worth a dime.";	[reply] [d/l] [select]
Re: Re: Re: Re: Backticks, $?, and Sudo by ignatz (Vicar) on Jan 17, 2003 at 21:14 UTC
So, alas, there's no way to get the result of the command that sudo runs? ()-() \"/ `	[reply]
Re: Re: Re: Re: Re: Backticks, $?, and Sudo by sauoq (Abbot) on Jan 17, 2003 at 21:26 UTC


Think about Loose Coupling
	PerlMonks