Get exit code from subshell through the pipes

Question

How can I get exit code of wget from the subshell process?

So, main problem is that $? is equal 0. Where can $?=8 be founded?

$> OUT=$( wget -q "http://budueba.com/net" | tee -a "file.txt" ); echo "$?"
0

It works without tee, actually.

$> OUT=$( wget -q "http://budueba.com/net" ); echo "$?"
8

But ${PIPESTATUS} array (I'm not sure it's related to that case) also does not contain that value.

$> OUT=$( wget -q "http://budueba.com/net" | tee -a "file.txt" ); echo "${PIPESTATUS[1]}"    

$> OUT=$( wget -q "http://budueba.com/net" | tee -a "file.txt" ); echo "${PIPESTATUS[0]}"
0

$> OUT=$( wget -q "http://budueba.com/net" | tee -a "file.txt" ); echo "${PIPESTATUS[-1]}"
0

So, my question is - how can I get wget's exit code through tee and subshell?

If it could be helpful, my bash version is 4.2.20.

score 24 · Accepted Answer · edited Mar 31 '23 at 09:38

24

By using $() you are (effectively) creating a subshell. Thus the PIPESTATUS instance you need to look at is only available inside your subshell (i.e. inside the $()), since environment variables do not propagate from child to parent processes.

You could do something like this:

  OUT=$( wget -q "http://budueba.com/net" | tee -a "file.txt"; exit ${PIPESTATUS[0]} );
  echo $? # prints exit code of wget.

You can achieve a similar behavior by using the following:

  OUT=$(wget -q "http://budueba.com/net")
  rc=$? # save exit code for later
  echo "$OUT" | tee -a "file.txt"

edited Mar 31 '23 at 09:38

0xC0000022L

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answered Feb 14 '12 at 13:42

Christian.K

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But is it possible to export all `${PIPESTATUS}` array up to parent shell? – ДМИТРИЙ МАЛИКОВ Feb 14 '12 at 13:49
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That is not how [`export`](http://www.gnu.org/software/bash/manual/bashref.html#Environment) works - it exports variables as environment variables for *child* processes (from the parent). – Christian.K Feb 14 '12 at 13:52
Here is a [solution for bringing the entire `${PIPESTATUS[@]}` array into the parent script](https://stackoverflow.com/questions/41716616/get-exit-codes-of-a-pipe-when-output-is-assigned-to-variable-command-substituti/44314883#44314883). It involves adding it to the end of the created variable and then pulling it off into a new array. – Adam Katz Jun 01 '17 at 21:10

score 6 · Answer 2 · answered Mar 17 '17 at 09:49

6

Beware of this when using local variables:

local OUT=$(command; exit 1)
echo $? # 0

OUT=$(command; exit 1)
echo $? # 1

answered Mar 17 '17 at 09:49

Mrskman

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Declaring `local OUT` then assigning `OUT=` on a new line correctly sets the exit code variable `$?` if you don't want scope creep. – William George Apr 05 '17 at 03:02
ShellCheck points out this exact issue, so simply heed the warning from ShellCheck and you should be good to go ... – 0xC0000022L Mar 31 '23 at 09:39

score 0 · Answer 3 · answered Mar 03 '23 at 11:01

For everyone using bash. I think that by far cleanest solution to both get output value and each exit status in pipe is this.

A one-time preparation. Enable lastpipe shell option. It allows to get value from the last command in pipe without using subshell. If you're in an interactive shell, also disable job control: set +m (The latter isn't needed for scripts - job control is disabled there by default.)
```
shopt -s lastpipe
set +m
```

read the value into your variable, and use PIPESTATUS naturally. E.g.

grep -E "\S" "file.txt" | sort | uniq | read -d '' RES
# 'read' exit status 1 means all input was read till EOF, we're OK with that
if (( PIPESTATUS[0] > 1 || PIPESTATUS[1] > 0 || PIPESTATUS[2] > 0 || PIPESTATUS[3] > 1 )); then
  echo "ERROR"
else
  echo "$RES"
fi

The above reads all non-empty lines from "file.txt", sorts them and removes duplicates. In this example we have custom processing of exit codes: grep exit status 1 means no lines were selected, we're OK with that; read exit status 1 is expected for saving multi-line output (at least, I don't know another clean way to do it). Clean means without cluttering the code just to avoid the exit status of 1 of read.

NOTE: the read -d '' option is used to read all the input into our variable (by disabling delimiter read stops at, which by default is a newline symbol). This is how we save multi-line output. If your pipe has just one line then you can use plain read RES (and likely can change expected exit status from read to 0 and not 1 as above).

score -1 · Answer 4 · edited May 23 '17 at 12:09

-1

Copy the PIPESTATUS array first. Any reads destroy the current state.

declare -a PSA  
cmd1 | cmd2 | cmd3  
PSA=( "${PIPESTATUS[@]}" )

I used fifos to solve the sub-shell/PIPESTATUS problem. See bash pipestatus in backticked command?
I also found these useful: bash script: how to save return value of first command in a pipeline?
and https://unix.stackexchange.com/questions/14270/get-exit-status-of-process-thats-piped-to-another/70675#70675

edited May 23 '17 at 12:09

Community

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answered Nov 02 '13 at 04:03

maxdev137

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The code you provided doesn't answer the question. If the multiple links have the answer about getting the result from sub shell + getting the exit codes then please provide an excerpt right in the answer. – Denis P Mar 06 '23 at 11:38

Get exit code from subshell through the pipes

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