Re: [Help-bash] difference of $? and ${PIPESTATUS[0]}

[felix]

Hi,

Comming on this very old thread:

On Wed, 4 Dec 2013 14:40:11 -0500, Greg Wooledge wrote:
> 
> The most obvious difference is that $? is shorter.
> 
> $? is also POSIX standard (older than POSIX in fact), so it works in sh
> scripts as well.  PIPESTATUS is a Bash extension.
> 
> Finally, note that if you execute a pipeline, $? will contain the exit
> status of the last command in the pipeline, not the first command,
> which is what ${PIPESTATUS[0]} would contain.  (If you execute a simple
> command instead of a pipeline, then they would both have the same value.)

Some asked on StackOverflow.com:
  Why does a Bash while loop result in PIPESTATUS "1" instead of "0"?
  https://stackoverflow.com/q/78351657/1765658

Then after some tests:

  if ls /wrong/path | wc | cat - /wrong/path | sed 'w/wrong/path' >/dev/null ; 
then
      echo Don't print this'
  fi ; echo ${?@Q} ${PIPESTATUS[@]@A}  $(( $? ${PIPESTATUS[@]/#/+} ))

  ls: cannot access '/wrong/path': No such file or directory
  cat: /wrong/path: No such file or directory
  sed: couldn't open file /wrong/path: No such file or directory
  '0' declare -a PIPESTATUS=([0]="2" [1]="0" [2]="1" [3]="4") 7

Where $PIPESTATUS[0]=>2 and $?=>0 !!

I could explain that '$?' is result of bash's if...then...fi group command
executed correctly and PIPESTATUS hold result of "most-recently-executed
foreground pipeline", but man page say:

    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).

     ?   Expands  to  the exit status of the most recently executed fore‐
         ground pipeline.

If so, "$?" have to be equivalent to "${PIPESTATUS[0]}", I think.

I suggest that man page should be modified to replace "foreground pipeline"
by "command" under "?" paragraph.


-- 
 Félix Hauri  -  <felix@f-hauri.ch>  -  http://www.f-hauri.ch