Do not fork for a subshell if it is the last thing this shell is doing

(EV_EXIT). The fork is still done as normal if any traps are active.

In many cases, the fork can be avoided even without this change by using {}
instead of (), but in practice many scripts use (), likely because the
syntax is simpler.

Example:
  sh -c '(/bin/sleep 10)& sleep 1;ps -p $! -o comm='
Now prints "sleep" instead of "sh". $! is more useful this way.
Most shells (dash, bash, pdksh, ksh93, zsh) seem to print "sleep" for this.

Example:
  sh -c '( ( ( (ps jT))))'
Now shows no waiting shell processes instead of four.
Most shells (dash, bash, pdksh, ksh93, zsh) seem to show zero or one.

PR:		bin/74404
Approved by:	ed (mentor) (implicit)

1 files changed, 2 insertions, 2 deletions

diff --git a/bin/sh/eval.c b/bin/sh/eval.c
index eeea605..c0b2096 100644
--- a/bin/sh/eval.c
+++ b/bin/sh/eval.c
@@ -401,8 +401,8 @@ evalsubshell(union node *n, int flags)
 	int backgnd = (n->type == NBACKGND);
 
 	expredir(n->nredir.redirect);
-	jp = makejob(n, 1);
-	if (forkshell(jp, n, backgnd) == 0) {
+	if ((!backgnd && flags & EV_EXIT && !have_traps()) ||
+			forkshell(jp = makejob(n, 1), n, backgnd) == 0) {
 		if (backgnd)
 			flags &=~ EV_TESTED;
 		redirect(n->nredir.redirect, 0);