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

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(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)
This commit is contained in:
Jilles Tjoelker 2009-06-23 21:50:06 +00:00
parent 73f4ccbd29
commit 4f6e4215a0
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=194774
1 changed files with 2 additions and 2 deletions
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4
bin/sh/eval.c
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@ -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);