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document workaround for the $(…) parsing bug

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tg 2010-09-05 19:12:24 +00:00
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@ -1,4 +1,4 @@
.\" $MirOS: src/bin/mksh/mksh.1,v 1.237 2010/08/28 21:22:24 tg Exp $
.\" $MirOS: src/bin/mksh/mksh.1,v 1.238 2010/09/05 19:12:24 tg Exp $
.\" $OpenBSD: ksh.1,v 1.136 2010/07/15 20:04:35 schwarze Exp $
.\"-
.\" Copyright © 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
@ -71,7 +71,7 @@
.\" with -mandoc, it might implement .Mx itself, but we want to
.\" use our own definition. And .Dd must come *first*, always.
.\"
.Dd $Mdocdate: August 28 2010 $
.Dd $Mdocdate: September 5 2010 $
.\"
.\" Check which macro package we use
.\"
@ -6032,33 +6032,40 @@ See the documentation, CVS, and web site for details.
.Sh CAVEATS
.Nm
only supports the Unicode BMP (Basic Multilingual Plane).
Pipelines are executed in subshells.
It has a different scope model from
.At
.Nm ksh ,
which leads to subtile differences in semantics for identical builtins.
.Pp
The parts of a pipeline, like below, are executed in subshells.
Thus, variable assignments inside them fail.
Use co-processes instead.
.Bd -literal -offset indent
foo \*(Ba bar \*(Ba read baz # will not change $baz
foo \*(Ba bar \*(Ba& read -p baz # will, however, do so
.Ed
.Sh BUGS
Suspending (using \*(haZ) pipelines like the one below will only suspend
the currently running part of the pipeline; in this example,
.Dq fubar
is immediately printed on suspension (but not later).
is immediately printed on suspension (but not later after an
.Ic fg ) .
.Bd -literal -offset indent
$ sleep 666 && echo fubar
.Ed
.Pp
Some parts of the parser are not recursive; things like the following
example will fail because of the parenthesis asymmetry:
Some parts of the parser are not recursive; the following
code fails because of the parenthesis asymmetry
.Pq RedHat BZ#496791 .
A workaround exists; use
.Ql x=$(cat) \*(Lt\*(Lt"EOF"
instead to merely slurp the string.
.Bd -literal -offset indent
x=$(case $foo in bar) echo $bar ;; *) echo $baz ;; esac)
.Ed
.Pp
Patches welcome.
.Pp
The parts of a pipeline, like below, are executed in subshells.
Thus, variable assignments inside them fail.
This is actually a feature; use co-processes instead.
.Bd -literal -offset indent
foo \*(Ba bar \*(Ba read baz # will not change $baz
# above fails to parse; below is the workaround
x=$(eval $(cat)) \*(Lt\*(Lt"EOF"
case $foo in bar) echo $bar ;; *) echo $baz ;; esac
EOF
.Ed
.Pp
This document attempts to describe