xref: /csrg-svn/local/toolchest/ksh/COMPATIBILITY (revision 35113)

			KSH-I VS. SH



I have not made a complete comparison between 5.2 /bin/sh and ksh-i.  A
direct comparison of the manuals may uncover more incompatibilities than
I have listed here.  In addition, I have omitted some incompatibilities
that are bugs in 5.0 sh that may have been fixed for 5.2.  I have
also omitted incompatibilities in cases that sh clearly is incorrect,
such as in cases where it core dumps. I have also omitted cases which
are bugs in ksh-i.  I have omitted built-ins in ksh-i which are not in /bin/sh
since this can be circumvented by using the alias facility if necessary.

The following is a list of known incompatibilities between ksh-i and sh:

1.	The IFS parameter is only effective for the read built-in and
	after parameter and command substitution in ksh-i.  Thus, IFS=x;
	exit will execute e on the file it with sh but will exit with ksh-i.

2.	If an environment parameter is modified by ksh-i, the new value
	will be passed to the children.  In sh you must export the
	parameter for this to happen.

3.	Time is a reserved word in ksh-i.  Thus time a | b will time the
	pipeline in ksh-i while only a will be timed with sh.  You can
	also time built-in commands and functions with ksh-i, you can't
	with sh.

4.	Select and function are reserved words in ksh-i.

5.	Parameter assignments only have scope for the command or function
	they precede in ksh-i.  Only a subset of built-in commands in ksh-i treat
	parameter assignments globally.  In sh, all built-in commands and
	functions treat parameter assignments as globals.  (Notice that 5.0
	and 5.2 treat parameter assignments to pwd and echo in an
	incompatible way).

6.	The output of some built-in commands and error messages is different
	in a few cases, for example times produces two lines of output in ksh-i.

7.	While loops with redirection are not executed in a separate process
	in ksh-i so assignments made within loops remain in effect after the
	loop completes.

8.	The semantics of functions are somewhat different.  Ksh-i can have
	local variables and allow recursive functions.  Errors in functions
	abort the function but not the script that they are in.

9.	The name space for functions and variables is separate in ksh-i.  In
	/bin/sh they share the same space. The unset builtin requires
	a -f flag to unset a function in ksh-i.

10.	Words that begin with ~ may be expanded in ksh-i. Sh does not have
	this feature.

11.	The character ^ is not special in ksh-i.  In sh it is an archaic
	synonym for |.

12.	Whenever (( occurs where a command name is valid, ksh-i assumes
	that an arithmetic expression follows.  In sh this means a
	sub-shell inside a sub-shell.

13.	Non-blank contiguous IFS delimiters generate a null input argument.
	Therefore, you can use IFS=: and correctly read the /etc/profile
	file even when fields are omitted.  In sh, multiple delimiters
	count as a single delimiter.

14.	Arithmetic test comparison operators (-eq, -lt, ...) allow any
	arithmetic expressions.  Sh allows only constants.  If you say
	test x -eq 0 in sh, which is meaningless, it returns true, but
	in ksh-i it depends on the value of the variable x.  If there
	is no variable x, then ksh-i produces an error message.

15.	The environment handed down to a program is not sorted in ksh-i.
	A user should not reply in this quirk of sh since any user
	program can provide an environment list which does not have
	to be sorted. (Getenv(3) does not assume a sorted list).

16.	There is an alias hash in ksh-i which does what the 5.2 has
	built-in hash does except for the -r flag.  In ksh-i, you must say
	PATH=$PATH to achieve the same result.

17.	The expansion of "$@" with no arguments produces the null string
	in the Bourne shell and produces nothing with ksh-i when there are
	no arguments.  I am not sure whether this is a bug in the Bourne
	shell or intentional.  The manual page leads me to think that it
	is a bug.  Set -- with no arguments unsets the positional parameter
	list in ksh-i.  Thus, scripts that use set -- "$@" when there are
	so positional parameters will not break.

18.	Ksh-i accepts options of the form -x -v as well as -xv both for
	invocation and for the set builtin.  The Bourne shell only allows
	one option parameter.

19.	Ksh-i does not allow unbalanced quotes with any script.  If the end of
	file is reached before a balancing quote in sh, it quietly inserts
	the balancing quote.  Ksh-i, behaves like sh for eval statements.

20.	Failures of any built-in command cause a script to abort in sh. Ksh-i
	scripts will only abort on errors in certainly documented built-ins.
	In this respect ksh-i treats most built-in commands semantically the
	same as non-builtin commands.

21.	The sequence $( is special in ksh-i.  In sh the sequence is illegal
	unless quoted.  When used with "", $( must be preceded by a \ in
	ksh-i to remove its special meaning.

22.	The built-in command exec when used without arguments (for I/O
	redirection), will close on exec each file unit greater than 2.

23.	Ksh-i has some added security features which may cause some setuid
	programs to stop working.  Whenever the real and effective uid
	of a shell program is different, ksh-i sets the -p mode which resets
	the PATH and omits user profiles.  The file /etc/suid_profile is
	executed instead of the ENV file.

I am interested in expanding this list so please let me know if you
uncover any others.