Checking return value of commands in pipe

btherl · #1 (**permalink**) 04-23-2007

Hi,

I am wondering how I can check the return value of all commands in a pipe such as

gzip -dc file.gz | sort -u > output.txt

If I run this sequence in bash and check $?, I get the return status from sort. But I want to know if the initial gzip failed.

Similarly for longer pipe chains, I want to know if any of the components returned an error status.

I don't mind if you give a solution for another shell such as tcsh. Any solution is great!

Thanks!

anbu23 · #2 (**permalink**) 04-23-2007

Code:

gzip -dc file.gz && sort -u > output.txt
echo $?

&& Only if gzip command is successful sort command is executed.

btherl · #3 (**permalink**) 04-23-2007

But I want the output of gzip to go into sort..

vino · #4 (**permalink**) 04-23-2007

See if PIPESTATUS helps. From man sh

Code:

       PIPESTATUS
              An array variable (see Arrays below) containing a  list  of  exit
              status  values  from  the processes in the most-recently-executed
              foreground pipeline (which may contain only a single command).

btherl · #5 (**permalink**) 04-23-2007

Thankyou vino! That looks perfect.

Thankyou anbu also for your suggestion!

qneill · #6 (**permalink**) 08-28-2008

But how does one do it in a shell that doesn't have PIPESTATUS? I know that autoconf (tool to install source on almost Unix that has lots of shell-independent logic in it) plays tricks with redirection and subshells to capture the return values from inner pipe commands. I just never took the time to reverse engineer it in my head to understand it.

Anyone?

qneill · #7 (**permalink**) 06-02-2009

At the risk of sounding like a hermit (talking to myself), I recently examined some of the configure scripts and saw several patterns:

There aren't many pipe commands after all, mostly simple sed calls
The tricks played with redirection are for logging and/or extracting return values from simple commands used inside of subshells

So the PIPESTATUS appears to be unique in the ability to extract return values from simple pipe commands.

Quote:

Originally Posted by qneill

But how does one do it in a shell that doesn't have PIPESTATUS? I know that autoconf (tool to install source on almost Unix that has lots of shell-independent logic in it) plays tricks with redirection and subshells to capture the return values from inner pipe commands....

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