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Re: Re: Backticks, $?, and Sudo

by ignatz (Vicar)
on Jan 17, 2003 at 18:12 UTC ( #227757=note: print w/ replies, xml ) Need Help??


in reply to Re: Backticks, $?, and Sudo
in thread Backticks, $?, and Sudo

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 ******************************************
I should have included this in the first place.
()-()
 \"/
  `


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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

    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.

    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

    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.";
    
      So, alas, there's no way to get the result of the command that sudo runs?
      ()-()
       \"/
        `
      

        Well, as I showed in my other post, sudo does return the exit status of the command it runs.

        Unfortunately, the case where the command returns 1 seems to be indistinguishable from the case where sudo returns 1. I guess that little bit of ambiguity could be a big bummer. You might be able to get around it on a case by case basis by using wrappers for your commands.

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

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