From: Greg Hurrell <greg.hurrell@...>
Date: 2007-03-15T16:35:05+09:00
Subject: Why does popen3 fork a grandchild?

So I wanted to know why the global variable $? wasn't being set to
reflect the exit status of the subprocess when using popen3; I checked
the list archives and saw that this has come up many times and that
the cause is that popen3 forks a child, then from the child forks
another, effectively a "grandchild" process.

One of the consequences is that the exit status is effectively thrown
away. The workarounds suggested in the archives are:

- don't use popen3; find an alternative

- instead of checking $? make sure that nothing is printed to the
standard err

- append the exit code to the standard error as the last line and
extract it later

- write a popen3 replacement that uses a child rather than a
grandchild

So I've tried the latter option but I'm still left with the
curiosity... why does popen3 use this child/grandchild model? What are
the advantages of it?

Cheers,
Greg