From: Jilles Tjoelker <jilles@stack.nl>
To: Stephane Chazelas <stephane.chazelas@gmail.com>
Cc: dash@vger.kernel.org
Subject: Re: command substitutions in $PS4
Date: Sun, 30 Nov 2014 21:42:18 +0100 [thread overview]
Message-ID: <20141130204218.GB1103@stack.nl> (raw)
In-Reply-To: <20141117214931.GA4601@chaz.gmail.com>
On Mon, Nov 17, 2014 at 09:49:32PM +0000, Stephane Chazelas wrote:
> [tested on current git head
> f6d4def4e27b13fab174e948b94cd10550d3e10e]
> Command substitution doesn't seem to work in $PS4 (used for
> xtrace prompt):
> $ PS4='$(date +%T)> ' dash -xc :
> dash: 1: Syntax error: end of file unexpected (expecting ")")
> And with the old syntax:
> $ PS4='`date +%T`> ' dash -xc :
> > :
> And with more than one command:
> $ PS4='`date +%T`> ' dash -xc ':;:'
> > :
> dash doesn't return and seems to go in a forking loop,
> presumably because the `date` there triggers another PS4
> expansion and so on recursively
> If I prevent the recursion with:
> --- a/src/eval.c
> +++ b/src/eval.c
> @@ -776,7 +776,15 @@ evalcommand(union node *cmd, int flags)
> int sep;
>
> out = &preverrout;
> +
> + /*
> + * reset xflag temporarily for command substitutions performed
> + * upon $PS4 expansion
> + */
> + xflag = 0;
> outstr(expandstr(ps4val()), out);
> + xflag = 1;
> +
> sep = 0;
> sep = eprintlist(out, varlist.list, sep);
> eprintlist(out, arglist.list, sep);
> $ PS4='`date +%T`> ' ./src/dash -xc ':;sleep 1; date'
> > :
> 21:43:47> sleep 1
> 21:43:48> date
> Mon Nov 17 21:43:48 GMT 2014
> The command substitution still fails upon the first expansion
> only. I quickly gave up trying to find out why as I found the
> code there hard to follow.
In FreeBSD sh, I have disabled command substitution in PS4 (POSIX does
not require it anyway). It is treated as a syntax error.
Talking about syntax errors, dash has a problem there as well. If there
is a syntax error in PS4 and set -x is enabled, it will not execute any
simple commands (assignments to PS4 cause an error and are subsequently
reverted). FreeBSD sh prints the error messages and subsequently uses
the raw unexpanded text.
--
Jilles Tjoelker
prev parent reply other threads:[~2014-11-30 20:42 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-17 21:49 command substitutions in $PS4 Stephane Chazelas
2014-11-30 20:42 ` Jilles Tjoelker [this message]
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