Re: _AS_DETECT_BETTER_SHELL speedup

[Alexandre Duret-Lutz]

>>> "Noah" == Noah Misch <address@hidden> writes:

 Noah> On Sat, Jan 29, 2005 at 02:07:53PM +0100, Alexandre Duret-Lutz wrote:
 >> However my understanding is that modern shells already detect
 >> these cases and perform the optimization by themselves.  I know
 >> for sure that Zsh has the machinery for this (along with some
 >> other hairy tricks to limit forks at other places), and, from
 >> what I can observe from the command line, so does Bash.  

 Noah> FWIW:

 Noah> $ echo $BASH_VERSION
 Noah> 2.05b.0(1)-release
 Noah> $ strace bash -c '(foo) 2>/dev/null' 2>&1 | grep clone
 Noah> clone(child_stack=0, 
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x4000fe28) 
= 25378
 Noah> $ strace bash -c '(exec foo) 2>/dev/null' 2>&1 | grep clone
 Noah> clone(child_stack=0, 
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x4000fe28) 
= 25382

Thanks, I didn't know how to show it.

 Noah> $ strace bash -c '{ exec foo; } 2>/dev/null' 2>&1 | grep clone

You probably meant

$ strace bash -c '{ foo; } 2>/dev/null' 2>&1 | grep clone
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, 
child_tidptr=0xb7f93bc8) = 19138

Because if you `exec' in {...} it kills the shell executing your script.
-- 
Alexandre Duret-Lutz