sh: Save/restore changed variables in optimized command substitution.

In optimized command substitution, save and restore any variables changed by
expansions (${var=value} and $((var=assigned))), instead of trying to
determine if an expansion may cause such changes.

If $! is referenced in optimized command substitution, do not cause jobs to
be remembered longer.

This fixes $(jobs $!) again, simplifies the man page and shortens the code.

1 files changed, 2 insertions, 5 deletions

diff --git a/bin/sh/sh.1 b/bin/sh/sh.1
index f6682e6..3b7f3d3 100644
--- a/bin/sh/sh.1
+++ b/bin/sh/sh.1
@@ -32,7 +32,7 @@
 .\"	from: @(#)sh.1	8.6 (Berkeley) 5/4/95
 .\" $FreeBSD$
 .\"
-.Dd June 10, 2011
+.Dd June 12, 2011
 .Dt SH 1
 .Os
 .Sh NAME
@@ -1536,10 +1536,7 @@ except that the built-in commands
 and
 .Ic trap
 return information about the main shell environment
-if they are the only command in a command substitution
-and the substitutions in the command cannot cause side effects
-(such as from assigning values to variables or referencing
-.Li $! ).
+if they are the only command in a command substitution.
 .Ss Arithmetic Expansion
 Arithmetic expansion provides a mechanism for evaluating an arithmetic
 expression and substituting its value.