The man-page of bash, and its behavior is different from what the revision to POSIX and Single Unix Specification says.

Below I refer to the specification taht can be accessed at <a href="http://www.UNIX-systems.org/version3/online.html">http://www.UNIX-systems.org/version3/online.html</a>, the locations are relative to <a href="http://www.opengroup.org/onlinepubs/SOME_NUMBER">http://www.opengroup.org/onlinepubs/SOME_NUMBER</a> after you login (free).


According to the specification
(utilities/sh.html#tag_04_128_04), intercarivity decision should be based on whether stdin and stderr are connected to a terminal, stdout is not important. But /bin/sh\'s decision is based on whether stdin and stdout is connected to a terminal, stderr is not taken into account.

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Running the test from utilities/sh.html#tag_04_128_16

1:

$ bash
$ echo $-
bhimBH
$ exit

Fine.


2:

$ bash &gt; o
echo $-
$ cat o
hB
$ bash 2&gt; o
bhimBH

bash doen\'t conform to POSIX: stdout and sterr roles are swapped.

3: 

$ /bin/sh &gt; o
echo $-
$ cat o
hB
$ /bin/sh 2&gt; o
echo $-
himB
$ cat o
sh-2.05a$ sh-2.05a$ exit

/bin/sh doesn\'t conform to POSIX, the same reason.

4:

$ /bin/sh --posix &gt; o
echo $-
$ cat o
hB
$ /bin/sh --posix 2&gt; o
echo $-
himB
$ 

/bin/sh --posix doen\'t conform to POSIX; the same reason.

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sh-2.05a-alt2