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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 $ .\" $OpenBSD: ksh.1,v 1.136 2010/07/15 20:04:35 schwarze Exp $
.\"- .\"-
.\" Copyright © 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 .\" 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 .\" with -mandoc, it might implement .Mx itself, but we want to
.\" use our own definition. And .Dd must come *first*, always. .\" 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 .\" Check which macro package we use
.\" .\"
@ -6032,33 +6032,40 @@ See the documentation, CVS, and web site for details.
.Sh CAVEATS .Sh CAVEATS
.Nm .Nm
only supports the Unicode BMP (Basic Multilingual Plane). only supports the Unicode BMP (Basic Multilingual Plane).
Pipelines are executed in subshells.
It has a different scope model from It has a different scope model from
.At .At
.Nm ksh , .Nm ksh ,
which leads to subtile differences in semantics for identical builtins. 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 .Sh BUGS
Suspending (using \*(haZ) pipelines like the one below will only suspend Suspending (using \*(haZ) pipelines like the one below will only suspend
the currently running part of the pipeline; in this example, the currently running part of the pipeline; in this example,
.Dq fubar .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 .Bd -literal -offset indent
$ sleep 666 && echo fubar $ sleep 666 && echo fubar
.Ed .Ed
.Pp .Pp
Some parts of the parser are not recursive; things like the following Some parts of the parser are not recursive; the following
example will fail because of the parenthesis asymmetry: code fails because of the parenthesis asymmetry
.Pq RedHat BZ#496791 .
A workaround exists; use
.Ql x=$(cat) \*(Lt\*(Lt"EOF"
instead to merely slurp the string.
.Bd -literal -offset indent .Bd -literal -offset indent
x=$(case $foo in bar) echo $bar ;; *) echo $baz ;; esac) x=$(case $foo in bar) echo $bar ;; *) echo $baz ;; esac)
.Ed # above fails to parse; below is the workaround
.Pp x=$(eval $(cat)) \*(Lt\*(Lt"EOF"
Patches welcome. case $foo in bar) echo $bar ;; *) echo $baz ;; esac
.Pp EOF
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
.Ed .Ed
.Pp .Pp
This document attempts to describe This document attempts to describe