The ksh(1) manual says that PPID should be read-only. But:
$ man ksh | grep PPID
PPID The process ID of the shell's parent (read-only).
$ echo ${PPID}
5967
$ PPID=123
$ echo ${PPID}
123
We can fix either the manual or ksh itself; this diff takes the latter
approach. It is tempting to do this with "typeset -ir PPID" but that
actually doesn't work:
$ FOO=123
$ typeset -ir FOO
ksh: FOO: is read only
So we fix this by putting "typeset -r PPID" on its own line. One could
imagine shortening the section below with something like:
"typeset", "-i", "PPID", "OPTIND=1", NULL,
"typeset", "-r", "KSH_VERSION", "PPID", NULL,
"typeset", "-x", "SHELL", "PATH", "HOME", NULL,
but that involves some reordering: the -i's MUST come before the -r's.
Index: bin/ksh/main.c
===================================================================
RCS file: /open/anoncvs/cvs/src/bin/ksh/main.c,v
retrieving revision 1.79
diff -u -p -r1.79 main.c
--- main.c 4 Mar 2016 15:11:06 -0000 1.79
+++ main.c 8 Sep 2016 13:17:29 -0000
@@ -85,6 +85,7 @@ static const char *initcoms [] = {
"typeset", "-r", "KSH_VERSION", NULL,
"typeset", "-x", "SHELL", "PATH", "HOME", NULL,
"typeset", "-i", "PPID", NULL,
+ "typeset", "-r", "PPID", NULL,
"typeset", "-i", "OPTIND=1", NULL,
"eval", "typeset -i RANDOM MAILCHECK=\"${MAILCHECK-600}\"
SECONDS=\"${SECONDS-0}\" TMOUT=\"${TMOUT-0}\"", NULL,
"alias",
