Date: Wed, 3 Jul 2013 21:22:47 +0000 (UTC) From: Jilles Tjoelker <jilles@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-9@freebsd.org Subject: svn commit: r252609 - stable/9/bin/sh Message-ID: <201307032122.r63LMlgV022204@svn.freebsd.org>
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Author: jilles Date: Wed Jul 3 21:22:47 2013 New Revision: 252609 URL: http://svnweb.freebsd.org/changeset/base/252609 Log: MFC r248692: sh(1): Mention possible ambiguities with $(( and ((. In some other shells, things like $((a);(b)) are command substitutions. Also, there are shells that have an extension ((ARITH)) that evaluates an arithmetic expression and returns status 1 if the result is zero, 0 otherwise. This extension may lead to ambiguity with two subshells starting in sequence. Modified: stable/9/bin/sh/sh.1 Directory Properties: stable/9/bin/sh/ (props changed) Modified: stable/9/bin/sh/sh.1 ============================================================================== --- stable/9/bin/sh/sh.1 Wed Jul 3 21:21:54 2013 (r252608) +++ stable/9/bin/sh/sh.1 Wed Jul 3 21:22:47 2013 (r252609) @@ -32,7 +32,7 @@ .\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95 .\" $FreeBSD$ .\" -.Dd November 5, 2011 +.Dd March 24, 2013 .Dt SH 1 .Os .Sh NAME @@ -1061,6 +1061,9 @@ A subshell environment may be implemente If job control is enabled in an interactive shell, commands grouped in parentheses can be suspended and continued as a unit. .Pp +For compatibility with other shells, +two open parentheses in sequence should be separated by whitespace. +.Pp The second form never forks another shell, so it is slightly more efficient. Grouping commands together this way allows the user to @@ -1604,6 +1607,16 @@ and .Ic times returns information about the same process if they are the only command in a command substitution. +.Pp +If a command substitution of the +.Li $( +form begins with a subshell, +the +.Li $( +and +.Li ( +must be separated by whitespace +to avoid ambiguity with arithmetic expansion. .Ss Arithmetic Expansion Arithmetic expansion provides a mechanism for evaluating an arithmetic expression and substituting its value.
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