CVS commit: src/bin/sh

["Robert Elz" <kre%netbsd.org@localhost>]

Module Name:    src
Committed By:   kre
Date:           Sat May 27 06:32:12 UTC 2017

Modified Files:
        src/bin/sh: sh.1 var.c

Log Message:
It turns out that most shells do not do variable value/attribute
inheritance when a variable is declared local, but instead leave
the local var unset (if not given a value) in the function.
Only ash derived shells do inheritance it seems.

So, to compensate for that, and get one step closer to making
"local" part of POSIX, so we can really rely upon it, a compromise
has been suggested, where "local x" is implementation defined
when it comes to this issue, and we add "local -I x" to specify
inheritance, and "local -N x" to specify "not" (something...)
(not inherited, or not set, or whatever you prefer to imagine!)
The option names took a lot of hunting to find something reasonable
that no shell (we know of) had already used for some other purpose...
The I was easy, but 'u' 'U' 'X' ... all in use somewhere.

This implements that (well, semi-) agreement.

While here, add "local -x" (which many other shells already have)
which causes the local variable to be made exported.  Not a lot
of gain in that (since "export x" can always be done immediately
after "local x") but it is very cheap to add and allows more other
scripts to work with out shell.

Note that while 'local x="${x}"' always works to specify inheritance
(while making the shell work harder), "local x; unset x" does not
always work to specify the alternative, as some shells have
"re-interpreted" unset of a local variable to mean something that
would best be described as "unlocal" instead - ie: after the unset
you might be back with the variable from the outer scope, rather
than with an unset local variable.

Also add "unset -x" to allow unsetting a variable without removing
any exported status it has.

There are gazillions of other options that are not supported here!


To generate a diff of this commit:
cvs rdiff -u -r1.143 -r1.144 src/bin/sh/sh.1
cvs rdiff -u -r1.53 -r1.54 src/bin/sh/var.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.