nonsensical error message when backgrounding invocation of wait builtin

[Steve Newcomb]

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:


root@zorba:/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
srn@coolheads.com
+1 910 363 4032