Here document / redirection / background process weirdness

[Martin Jackson]

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-unknown-linux-gnu'
-DCONF_VENDOR='unknown'
-DLOCALEDIR='/home/mjackson/src/bash-4.2/_install/share/locale'
-DPACKAGE='bash' -DSHELL -DHAVE_CONFIG_H   -I.  -I. -I./include -I./lib
-g -O2
uname output: Linux stagecoach 3.5.0-25-generic #39-Ubuntu SMP Mon Feb 25
18:26:58 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
Machine Type: x86_64-unknown-linux-gnu

Bash Version: 4.2
Patch Level: 0
Release Status: release

Description:
When executing a here document in bash, with the here document piped to
another instance of bash, where the here document contains "echo <&- &;
wait", the here document gets executed twice. I have seen this on Ubuntu
both with the current 4.2.37 from ubuntu and the latest bash tarball
(details above)

Repeat-By:
    #!/home/mjackson/src/bash-4.2/_install/bin/bash

    /home/mjackson/src/bash-4.2/_install/bin/bash <<EOF
    declare -i a=0
    echo BASHPID is \$BASHPID
    true </dev/null & wait # NOP
    let a++
    echo a is \$a, BASHPID is \$BASHPID
    EOF

    Prints:
    BASHPID is 30866
    a is 1, BASHPID is 30866
    a is 2, BASHPID is 30866

Fix:
    Adding a manual 'exit' statement at the end of the here document seems
to be a workaround:

    #!/home/mjackson/src/bash-4.2/_install/bin/bash

    /home/mjackson/src/bash-4.2/_install/bin/bash <<EOF
    declare -i a=0
    echo BASHPID is \$BASHPID
    true </dev/null & wait # NOP
    let a++
    echo a is \$a, BASHPID is \$BASHPID
    exit
    EOF

    Prints:
    BASHPID is 30895
    a is 1, BASHPID is 30895