5 Jan
2023
5 Jan
'23
1:33 a.m.
On 1/4/23 11:15 AM, Dan Cross wrote:
On Tue, Jan 3, 2023 at 11:16 PM Bakul Shah
<bakul(a)iitbombay.org> wrote:
On Illumos, /bin/sh and /usr/xpg4/bin/sh are both links to ksh93.
ksh88/ksh93 and zsh are the only shells that unconditionally run the last
element of a pipeline in the current shell. Bash will do it if job control
is not enabled and the `lastpipe' option is enabled.
It's usually not a problem, but you do have to be aware of potential side
effects.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU chet(a)case.edu http://tiswww.cwru.edu/~chet/
On Jan 3, 2023, at 7:31 PM, Dan Cross
<crossd(a)gmail.com> wrote:
Interesting. In my testing, `bash` was the odd man out:
: doctor; zsh
: doctor; echo ' hi ' | sed 's/^ *//;s/ *$//' | read bummer
echo $bummer
hi
: doctor;
: doctor; bash
: doctor; echo ' hi ' | sed 's/^ *//;s/ *$//' | read bummer
echo $bummer
: doctor;
exit
: doctor; ksh
: doctor; echo ' hi ' | sed 's/^ *//;s/ *$//' | read bummer
: doctor; echo $bummer
hi
: doctor;
: doctor; sh
: doctor; echo ' hi ' | sed 's/^ *//;s/ *$//' | read bummer
: doctor; echo $bummer
hi
: doctor;
: doctor;
That's on illumos. On Tue, Jan 3, 2023 at 10:22 PM John Cowan
<cowan(a)ccil.org> wrote:
On this example sh, zsh, bash behave the same way on
freebsd. Rather than ban |, I think the lesson is to
*avoid* builtin commands in a pipeline that can affect
shell's environment. I only write /bin/sh scripts in
any case. Making shell scripts portable means not using
pipelines, because given "foo | bar", kshNN and zsh execute foo in a subshell
and bar in the top-level shell, whereas in other shells, both foo and bar execute in
subshells. (For this reason, Posix allows either behavior.) Not having pipelines is a
pretty drastic limitation.
This came up at work just the other day:
echo ' hi ' | sed 's/^ *//;s/ *$//' | read bummer
echo $bummer
The behavior varies between ksh, zsh, bash, sh. Yay.