unix shell, getting exit code with piped child

Question

Let's say I do this in a unix shell

$ some-script.sh | grep mytext

$ echo $?

this will give me the exit code of grep

but how can I get the exit code of some-script.sh

EDIT

Assume that the pipe operation is immutable. ie, I can not break it apart and run the two commands seperately

score 5 · Accepted Answer · answered May 17 '10 at 18:29

5

There are multiple solutions, it depends on what you want to do exactly.

The easiest and understandable way would be to send the output to a file, then grep for it after saving the exit code:

tmpfile=$(mktemp)
./some-script.sh > $tmpfile
retval=$?
grep mytext $tmpfile
rm tmpfile

answered May 17 '10 at 18:29

watain

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3

I see. Maybe that's a solution: `tmpfile=$(mktemp); (./some-script.sh; echo $? > $tmpfile) | grep mytext; retval=$(cat $tmpfile)`. That's quite dirty, but maybe it helps. – watain May 17 '10 at 18:35
then grep gets the output of `echo $? > tmpfile` – Mike May 17 '10 at 18:43
No, because `echo $? > $tmpfile` has no output. The standard output of `echo` is sent to `$tmpfile`. – watain May 17 '10 at 18:47
right, and that nothing gets passed to grep, it doesn't append the output of the first command – Mike May 17 '10 at 18:48
I'm not sure if I understood that correctly. The output of the first command (`./some-script.sh`) still reaches grep. Have you tried it? Maybe you could add the actual script with the problem and why the pipe operation is immutable. – watain May 17 '10 at 18:57

score 4 · Answer 2 · answered Jan 25 '11 at 06:04

A trick from the comp.unix.shell FAQ (#13) explains how using the pipeline in the Bourne shell should help accomplish what you want:

   You need to use a trick to pass the exit codes to the main
   shell.  You can do it using a pipe(2). Instead of running
   "cmd1", you run "cmd1; echo $?" and make sure $? makes it way
   to the shell.

   exec 3>&1
   eval `
     # now, inside the `...`, fd4 goes to the pipe
     # whose other end is read and passed to eval;
     # fd1 is the normal standard output preserved
     # the line before with exec 3>&1
     exec 4>&1 >&3 3>&- 
     {
       cmd1 4>&-; echo "ec1=$?;" >&4
     } | {
       cmd2 4>&-; echo "ec2=$?;" >&4
     } | cmd3
     echo "ec3=$?;" >&4

score 2 · Answer 3 · edited Nov 11 '12 at 13:03

2

There is a utility named mispipe which is part of the moreutils package.

It does exactly that: mispipe some-script.sh 'grep mytext'

edited Nov 11 '12 at 13:03

Bakuriu

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answered Nov 11 '12 at 12:37

someone

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score 2 · Answer 4 · answered May 17 '10 at 18:32

2

If you're using bash:

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

answered May 17 '10 at 18:32

Randy Proctor

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I'm using sh. My client doesn't like bash – Mike May 17 '10 at 18:34

score 0 · Answer 5 · answered Aug 23 '13 at 07:23

First approach, temporarly save exit status in some file. This cause you must create subshell using braces:

(your_script.sh.pl.others; echo $? >/tmp/myerr)|\ #subshell with exitcode saving
grep sh #next piped commands
exitcode=$(cat /tmp/myerr) #restore saved exitcode
echo $exitcode  #and print them

another approach presented by Randy above, simplier code implementation:

some-script.sh | grep mytext
echo ${PIPESTATUS[0]} #print exitcode for first commands. tables are indexted from 0

its all. both works under bash (i know, bashizm). good luck :) both approaches does not save temporarly pipe to physical file, only exit code.

unix shell, getting exit code with piped child

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