CentOS - May 2011 - Getting the return value of the last command run

All commands return a value, usually 0 if run properly. For instance, try:
$ ls && echo "done"
$ lsd && echo "done"

The echo command is only executed if the ls command exited
successfully. If one did not add the echo command with the && after a
command, how can he determine if the command exited successfully? I
have a particularly troubling script that gives does not mention if it
exits successfully or not. I could modify it (and probably will some
day) but in general I'd like to know the answer to this question as a
learning experience.

Thanks.

-- 
Dotan Cohen

http://gibberish.co.il
http://what-is-what.com

On Mon, May 30, 2011 at 10:38 AM, Dotan Cohen <dotancohen at gmail.com>
wrote:
> All commands return a value, usually 0 if run properly. For instance, try:
> $ ls && echo "done"
> $ lsd && echo "done"
>
> The echo command is only executed if the ls command exited
> successfully. If one did not add the echo command with the && after
a
> command, how can he determine if the command exited successfully?
You can check the return code.

$ ls
$ echo $?

0 (usually) indicates success.

- Bob

Have a read up on using return codes in Bash.

http://tldp.org/LDP/abs/html/exit-status.html

<http://tldp.org/LDP/abs/html/exit-status.html>Quick example:

#!/bin/bash

ls foobar

   if [ $? -eq 0 ] ; then
      echo "successful"
   else
      echo "not successful"
   fi

You get the idea..

Cheers,
Chris


On 30 May 2011 15:38, Dotan Cohen <dotancohen at gmail.com> wrote:
> All commands return a value, usually 0 if run properly. For instance, try:
> $ ls && echo "done"
> $ lsd && echo "done"
>
> The echo command is only executed if the ls command exited
> successfully. If one did not add the echo command with the && after
a
> command, how can he determine if the command exited successfully? I
> have a particularly troubling script that gives does not mention if it
> exits successfully or not. I could modify it (and probably will some
> day) but in general I'd like to know the answer to this question as a
> learning experience.
>
> Thanks.
>
> --
> Dotan Cohen
>
> http://gibberish.co.il
> http://what-is-what.com
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> http://lists.centos.org/mailman/listinfo/centos
>


-- 
Kind Regards,
Christopher J. Buckley
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.centos.org/pipermail/centos/attachments/20110530/e4c11e0d/attachment-0005.html>

On Mon, 30 May 2011, Christopher J. Buckley wrote:
> To: CentOS mailing list <centos at centos.org>
> From: Christopher J. Buckley <chris at cjbuckley.net>
> Subject: Re: [CentOS] Getting the return value of the last command run
> 
> Have a read up on using return codes in Bash.
>
> http://tldp.org/LDP/abs/html/exit-status.html
>
> <http://tldp.org/LDP/abs/html/exit-status.html>Quick example:
>
> #!/bin/bash
>
> ls foobar
>
>   if [ $? -eq 0 ] ; then
>      echo "successful"
>   else
>      echo "not successful"
>   fi
>
> You get the idea..
>
> Cheers,
> Chris
Excellent Bash tutorial and reference with loads of working 
examples. I whole-heartedly recommend it and there are 
different versions such as PDF format under:

http://tldp.org/LDP/abs/

Kind Regards,

Keith Roberts

-----------------------------------------------------------------
Websites:
http://www.karsites.net
http://www.php-debuggers.net
http://www.raised-from-the-dead.org.uk

All email addresses are challenge-response protected with
TMDA [http://tmda.net]
-----------------------------------------------------------------

On Mon, May 30, 2011 at 17:59, Christopher J. Buckley
<chris at cjbuckley.net> wrote:
> Have a read up on using return codes in Bash.
> http://tldp.org/LDP/abs/html/exit-status.html
Thanks, Chris, the link was very informative. I should spend more time
at the tldp site, I know.


-- 
Dotan Cohen

http://gibberish.co.il
http://what-is-what.com

On Mon, May 30, 2011 at 05:38:56PM +0300, Dotan Cohen
wrote:
> All commands return a value, usually 0 if run properly. For instance, try:
> $ ls && echo "done"
> $ lsd && echo "done"
> 
> The echo command is only executed if the ls command exited
> successfully. If one did not add the echo command with the && after
a
> command, how can he determine if the command exited successfully? I
> have a particularly troubling script that gives does not mention if it
> exits successfully or not. I could modify it (and probably will some
> day) but in general I'd like to know the answer to this question as a
> learning experience.
Yes, all commands return a value UNLESS it was written by one of the
idi,... er, misguided programmers who thinks its ok to write (in 
C):

void main (void)
	{
	...
	exit();
	}

because, of course, in C main() always returns SOMETHING.

I'm sure it's the same in a bash script, even if the script doesn't
explicitly provide a return value I imagine the shell returns something
anyway, it's just that it's meaningless when that happens.

-- 
---- Fred Smith -- fredex at fcshome.stoneham.ma.us
-----------------------------
                       I can do all things through Christ 
                              who strengthens me.
------------------------------ Philippians 4:13 -------------------------------