Get exit code from subshell through the pipes

问题

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.

回答1:

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

回答2:

Beware of this when using local variables:

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

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

回答3:

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

来源：https://stackoverflow.com/questions/9277827/get-exit-code-from-subshell-through-the-pipes

标签

bash

pipe

exit-code

tee

subshell