--------
Historical notes for osh(1) and sh6(1):

The Thompson shell, by Ken Thompson of Bell Labs, was distributed
as the standard command interpreter through Sixth Edition Unix.
Then, in the Seventh Edition, it was replaced by the Bourne shell.
However, the Thompson shell was still distributed with the system
as osh because of known portability problems with the Bourne shell's
memory management in Seventh Edition Unix.

The name of the Thompson shell's binary executable was `sh'.
It was installed as `/bin/sh' through Sixth Edition Unix and
made use of the following external utilities:

	1) /bin/exit was used to terminate command files.

	2) /bin/goto was used to transfer the shell's control
	   from one point to another within a command file.

	3) /bin/if was used to evaluate conditional expressions.
	   This is the predecessor of test(1), which was first
	   released in Seventh Edition Unix.

	4) /etc/glob was used to expand `*', `?', and `[...]'
	   in command arguments.

The functionality of each of the above-mentioned utilities is
provided here.  However, the `exit' utility is implemented as a
special built-in command.  See the goto(1) and if(1) manual pages
for full details regarding the ports of these utilities.

For osh(1), `glob' is built into the shell by using a port of the
glob6(1) source code.

For sh6(1), the Thompson-shell port's binary executable has been
renamed from `sh' to `sh6' to avoid name conflict and confusion
with the system shell, sh(1), on modern Unix systems.  Similarly,
the `glob' utility has been renamed to `glob6' and is installed
into the same directory as the shell, rather than being installed
into the /etc directory.

--------
Compatibility notes for osh(1):

This is an enhanced, backward-compatible port of the Thompson shell
from Sixth Edition Unix.  However, when it is known to differ in
some way from the original, this fact is indicated in the osh(1)
manual page.

Aside from those differences which are detailed either in the manual
page or below, the only other substantial difference is that this
port of the shell can handle 8-bit character sets.  However, the
original can only handle 7-bit ASCII.

Further details regarding some of the known differences:

1) This port of the shell uses PATH to search for external commands,
   but the original always uses the equivalent of `.:/bin:/usr/bin'.
   The sh(1) manual page from Sixth Edition Unix reads as follows:

       If  the  first argument is the name of an executable file,
       it is invoked; otherwise the string `/bin/'  is  prepended
       to  the  argument.   (In  this way most standard commands,
       which reside in `/bin', are found.)  If no such command is
       found,  the  string  `/usr'  is further prepended (to give
       `/usr/bin/command') and another attempt is made to execute
       the resulting file.  (Certain lesser-used commands live in
       `/usr/bin'.)

   ...
   The primary reason this port of the shell uses PATH instead of a
   procedure like that described above is for both user convenience
   and security.  The behavior described above can conceivably be
   quite dangerous as an unchangeable default.

   Using PATH allows the user to choose the search behavior.
   If search behavior like that of the original is desired, the
   user can set PATH to a value of `.:/bin:/usr/bin' in order to
   accomplish this.

2) This port of the shell ignores the first line of a command file
   if it begins with `#!' in order to play nicely with kernels which
   support the `#!' mechanism.  For example, the first line might be
   `#!/usr/local/bin/osh' or `#!/usr/bin/env osh'.  This is just for
   user convenience in the face of conflicting shell languages.

3) The original implementation of the shell does shell accounting
   in order to record command execution data; this one does not.

--------
Compatibility notes for sh6(1):

This is a port of the Thompson shell from Sixth Edition Unix.
However, when it is known to differ in some way from the original,
this fact is indicated in the sh6(1) manual page.

Aside from those differences which are detailed either in the manual
page or below, the CHANGES_sh-to-sh6 file contains further information
regarding how this port differs from the original.

Further details regarding the substantial differences:

1) This port of the shell uses PATH to search for external commands,
   but the original always uses the equivalent of `.:/bin:/usr/bin'.
   The sh(1) manual page from Sixth Edition Unix reads as follows:

       If  the  first argument is the name of an executable file,
       it is invoked; otherwise the string `/bin/'  is  prepended
       to  the  argument.   (In  this way most standard commands,
       which reside in `/bin', are found.)  If no such command is
       found,  the  string  `/usr'  is further prepended (to give
       `/usr/bin/command') and another attempt is made to execute
       the resulting file.  (Certain lesser-used commands live in
       `/usr/bin'.)

   ...
   The primary reason this port of the shell uses PATH instead of a
   procedure like that described above is for both user convenience
   and security.  The behavior described above can conceivably be
   quite dangerous as an unchangeable default.

   Using PATH allows the user to choose the search behavior.
   If search behavior like that of the original is desired, the
   user can set PATH to a value of `.:/bin:/usr/bin' in order to
   accomplish this.

2) This port of the shell ignores the first line of a command file
   if it begins with `#!' in order to play nicely with kernels which
   support the `#!' mechanism.  For example, the first line might be
   `#!/usr/local/bin/sh6' or `#!/usr/bin/env sh6'.  This is just for
   user convenience in the face of conflicting shell languages.

3) The original implementation of the shell does shell accounting
   in order to record command execution data; this port does not.

Jeffrey Allen Neitzel						2007/01/28