# Rescuing a failed %x\[\] call? **URL:** \ **Category:** Ruby\ **Created:** [December 4, 2008, 12:09am UTC](https://www.ruby-forum.com/t/rescuing-a-failed-x-call/154793 "2008-12-04T00:09:08Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![kyle\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kyle\_s](https://www.ruby-forum.com/u/kyle_s)\ **Post date:** [December 4, 2008, 12:09am UTC](https://www.ruby-forum.com/t/rescuing-a-failed-x-call/154793/1 "2008-12-04T00:09:08Z")
I know it should be streightforward, but I’m not finding the docs anywhere… How does one go about rescuing a failed shell command? like in the instance it fails, or the command isn’t found? Thanks, Kyle ---
**Author:** ![kyle\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kyle\_s](https://www.ruby-forum.com/u/kyle_s)\ **Post date:** [December 4, 2008, 4:34am UTC](https://www.ruby-forum.com/t/rescuing-a-failed-x-call/154793/2 "2008-12-04T04:34:38Z")
On Wed, Dec 3, 2008 at 6:02 PM, Kyle S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I know it should be streightforward, but I’m not finding the docs anywhere… > > How does one go about rescuing a failed shell command? like in the > instance it fails, or the command isn’t found? According to some experiments in IRB, the failed shell command won’t raise an exception; it will leave a non-zero exit code in the $? special variable. You’ll need to check the value of $? and take action accordingly. – Avdi Home: [http://avdi.org](http://avdi.org) Developer Blog: [Avdi Grimm, Code Cleric](http://avdi.org/devblog/) Twitter: [http://twitter.com/avdi](http://twitter.com/avdi) Journal: [http://avdi.livejournal.com](http://avdi.livejournal.com) ---
**Author:** ![kyle\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kyle\_s](https://www.ruby-forum.com/u/kyle_s)\ **Post date:** [December 4, 2008, 3:05pm UTC](https://www.ruby-forum.com/t/rescuing-a-failed-x-call/154793/3 "2008-12-04T15:05:12Z")
On Wed, Dec 3, 2008 at 9:28 PM, Avdi G. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > According to some experiments in IRB, the failed shell command won’t > raise an exception; it will leave a non-zero exit code in the $? > special variable. You’ll need to check the value of $? and take > action accordingly. > > – > Avdi Advi, the problem is I’ve got a script failing on a “command not found”, and not continuing onward. I see no amount of fiddling that can help that. ---
**Author:** ![kyle\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kyle\_s](https://www.ruby-forum.com/u/kyle_s)\ **Post date:** [December 4, 2008, 4:49am UTC](https://www.ruby-forum.com/t/rescuing-a-failed-x-call/154793/4 "2008-12-04T04:49:16Z")
From: Kyle S. [[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)] # I know it should be streightforward, but I’m not finding the # docs anywhere… what is kernel#system? ## botp@botp-desktop:~$ qri kernel#system ------------------------------------------------ Kernel#system system(cmd [, arg, …]) =\> true or false Executes cmd in a subshell, returning true if the command was found and ran successfully, false otherwise. An error status is available in $?. The arguments are processed in the same way as for Kernel::exec. ``` system("echo *") system("echo", "*") ``` # How does one go about rescuing a failed shell command? # like in the instance it fails, or the command isn’t found? basically, you’ll just have to ask it, like rescue\_command\_here unless system(my\_shell\_command) lastly, you’ll have to test it (because i just type this answers on my inbox w/o testing 🙂 ---
**Author:** ![kyle\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kyle\_s](https://www.ruby-forum.com/u/kyle_s)\ **Post date:** [December 4, 2008, 3:51pm UTC](https://www.ruby-forum.com/t/rescuing-a-failed-x-call/154793/5 "2008-12-04T15:51:44Z")
On Thu, Dec 4, 2008 at 8:58 AM, Kyle S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Advi, the problem is I’ve got a script failing on a “command not > found”, and not continuing onward. I see no amount of fiddling that > can help that. You may need to use IO.popen() instead, then. – Avdi Home: [http://avdi.org](http://avdi.org) Developer Blog: [Avdi Grimm, Code Cleric](http://avdi.org/devblog/) Twitter: [http://twitter.com/avdi](http://twitter.com/avdi) Journal: [http://avdi.livejournal.com](http://avdi.livejournal.com) ---
**Author:** ![kyle\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kyle\_s](https://www.ruby-forum.com/u/kyle_s)\ **Post date:** [December 4, 2008, 5:52pm UTC](https://www.ruby-forum.com/t/rescuing-a-failed-x-call/154793/6 "2008-12-04T17:52:15Z")
On Thu, Dec 4, 2008 at 8:58 AM, Kyle S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Advi, the problem is I’ve got a script failing on a “command not > found”, and not continuing onward. I see no amount of fiddling that > can help that. Just tried it… it works fine for me, outputs the “command not found” message on stderr but keeps right on going… what platform are you on? – Avdi Home: [http://avdi.org](http://avdi.org) Developer Blog: [Avdi Grimm, Code Cleric](http://avdi.org/devblog/) Twitter: [http://twitter.com/avdi](http://twitter.com/avdi) Journal: [http://avdi.livejournal.com](http://avdi.livejournal.com) ---
**Author:** ![kyle\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kyle\_s](https://www.ruby-forum.com/u/kyle_s)\ **Post date:** [December 4, 2008, 7:16pm UTC](https://www.ruby-forum.com/t/rescuing-a-failed-x-call/154793/7 "2008-12-04T19:16:17Z")
On Thu, Dec 4, 2008 at 10:45 AM, Avdi G. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Just tried it… it works fine for me, outputs the “command not found” > message on stderr but keeps right on going… what platform are you > on? > > – > Avdi Linux, CentOS/RedHat. Depending on the box it’ll be anywhere from 2.1AS all the way through 5.2, so the code is actually run on a rather wide variety. –Kyle ---
**Author:** ![kyle\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kyle\_s](https://www.ruby-forum.com/u/kyle_s)\ **Post date:** [December 4, 2008, 3:06pm UTC](https://www.ruby-forum.com/t/rescuing-a-failed-x-call/154793/8 "2008-12-04T15:06:58Z")
On Wed, Dec 3, 2008 at 9:42 PM, Peña, Botp [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Executes cmd in a subshell, returning true if the command was > > basically, you’ll just have to ask it, like > > rescue\_command\_here unless system(my\_shell\_command) > > lastly, you’ll have to test it (because i just type this answers on my inbox w/o testing 🙂 Would work, but I can’t use system because I need to capture and process the output of the shell commands. Thanks though.