Xref: utzoo comp.unix.questions:9591 comp.unix.wizards:11569
Path: utzoo!utgpu!attcan!uunet!steinmetz!davidsen
From: davidsen@steinmetz.ge.com (William E. Davidsen Jr)
Newsgroups: comp.unix.questions,comp.unix.wizards
Subject: {} grouping in sh and ksh
Message-ID: <12306@steinmetz.ge.com>
Date: 5 Oct 88 13:57:09 GMT
Reply-To: davidsen@crdos1.UUCP (bill davidsen)
Followup-To: comp.unix.wizards
Organization: GE Corp. R & D, Schenectady,NY
Lines: 31


  I recently posted an answer to a question and have been told that me
reply is true for ksh, but not for sh. Let me clarify the action of both
shells. I tested the sh operation on both V.2 and V7, so I am reasonably
certain of the action.

  In sh, actions grouped by {} delimiters will be treated as a unit and
may be used with &&, ||, and redirection. If redirection is used the
commands will be executed in a subshell. After the commands have been
run, if a subshell is not used the working directory is reset, such that
it always works as if a subshell were used.
  Ex:	{ cd ..; ps -l; pwd; ps -l; } && pwd
	{ cd ..; ps -l; pwd; ps -l; } > x && pwd

In the example with redirection the first ps will show a subshell
running.

  Even if a subshell is used, the last command is execed without a
fork, so the second ps will *never* show a subshell. This muddied the
water when I was investigating the action.

  In ksh a subshell is never used. After execution of the commands the
working directory is not reset. This is exactly as documented. The
examples above will produce the same output.

  I apologize if this mislead anyone, I know how ksh works, and a simple
test with sh before my last posting didn't show the details.
-- 
	bill davidsen		(wedu@ge-crd.arpa)
  {uunet | philabs}!steinmetz!crdos1!davidsen
"Stupidity, like virtue, is its own reward" -me