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nonsensical error message when backgrounding invocation of wait builtin


From: Steve Newcomb
Subject: nonsensical error message when backgrounding invocation of wait builtin
Date: Wed, 30 Dec 2009 21:29:57 -0500
User-agent: Thunderbird 2.0.0.23 (X11/20090817)

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-pc-linux-gnu' -DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL -DHAVE_CONFIG_H -I. -I../bash -I../bash/include -I../bash/lib -g -O2 -Wall uname output: Linux zorba 2.6.28-16-generic #57-Ubuntu SMP Wed Nov 11 09:49:32 UTC 2009 x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 3.2
Patch Level: 48
Release Status: release

Description:
It probably never makes sense to background the "wait" builtin, but if one makes this error, the
   resulting error message is nonsensical and confusing:

   wait: pid nnnnn is not a child of this shell ## (where nnnnn is the pid)

Repeat-By:

   E.g.:

#!/bin/bash
stdinFile=/tmp/stdin.$$
echo "echo \"here we are!\" ; sleep 3 ;" > $stdinFile
bashCommand=`cat $stdinFile`

/bin/bash -s <$stdinFile &        ## it doesn't matter which
# /bin/bash -c "$bashCommand" &   ## of these two lines is uncommented
pidOfBackgroundProcess=$! ;
echo "pidOfBackgroundProcess=$pidOfBackgroundProcess" ;
wait $pidOfBackgroundProcess & ## the ampersand here is the error that triggers the nonsensical error message

The typescript of an actual run of the above script looked like this:


address@hidden:/home/srn# /tmp/z.sh
here we are!
pidOfBackgroundProcess=20944
/tmp/z.sh: line 10: wait: pid 20944 is not a child of this shell

(But, of course, pid 20944 *was* in fact a child of this shell.)

Fix:

Never background an invocation of the wait builtin, accidentally or otherwise. (Unfortunately, I'm not always alert enough to avoid doing this, and I suspect there
       are others like me.)


Steve Newcomb
address@hidden
+1 910 363 4032





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