/bin/sh => STDIN & functions, var scope messing

[rank1seeker at gmail.com]

Redirections > and >> don't put it in a subshell.
Only pipe |, which means only STDIN affects/triggers this behaviour.
Does < operator also does it, as it is also STDIN?

Anyway, I don't care for executing binaries, but I do care if that is part of sh's code, as function is.
It messes var scopes.

And finally if we take into account this:

> For example… in pc-sysinstall…
> 
> ./backend/functions-extractimage.sh-      tar cvf - . 2>/dev/null | tar -xpv -C ${FSMNT} ${TAROPTS} -f - 2>&1 | tee -a ${FSMNT}/.tar-extract.log
> ./backend/functions-extractimage.sh:      if [ $? -ne 0 ]
> 
> That's a big no-no.
> 
> If your first tar (the initial lvalue to the first pipe) fails… but your second tar succeeds (rvalue to the first pipe)… you won't catch that failure in your checking of $?
> 
> Also, if the first tar succeeds, but the second tar fails, AND the final rvalue (the tee) succeeds… you also miss the error code.
> 
> I call this the "piped return-status conflation issue". Basically… anytime you want to check the return-status in shell… and you care about lvalue-failures in a pipe-chain… you must rewrite it to either:
> 
> (a) be aware of the problem (I've in the past written wrappers that will test the previous return status and abort the chain in such an event)
> 
> (b) undo the pipe-chain and store your results for incremental processing… checking the return status after each filter.
> 
> -- 
> Devin


sh's behaviour must be changed regarding pipeing

> > Curious. Which of the two behaviours is POSIXly correct?
> 
> Both. As per XCU 2.12 Shell Execution Environment, each command in a
> multi-command pipeline may or may not be executed in a subshell
> environment.
> 
> Behaviour different from our sh is most often encountered in the various
> versions of the real Korn shell (ksh88 and ksh93), which execute the
> last command in a pipeline in the current shell environment.
> 
> If things like  jobs | cat  work, that can also be explained using this
> rule.
> 
> -- 
> Jilles Tjoelker
>


Domagoj Smolčić