Re: [PATCH 6/6] use print or printf or cat as $ECHO

[Ralf Wildenhues]

Hello,

* Eric Blake wrote on Mon, Nov 10, 2008 at 05:30:27PM CET:
> Paolo Bonzini <bonzini <at> gnu.org> writes:
> 
> > 1) these tests do cost a few subshells (which can be as expensive as a
> > fork on bash, even if the executed command is a builtin).  In the
> > attached patch I conditionalized it on ${TMOUT} so that it is not
> > executed unless we're on ksh.

> Your filter based on TMOUT is different 
> than my filter on {BASH,ZSH}_VERSION; I could go either way (I tested that 
> pdksh also supplies both $TMOUT and print).

Who guarantees you that ksh supplies TMOUT?  OTOH, TMOUT is not in any
way restricted, so a user (more likely: a sysadmin) could set and export
it, and reasonably so: every Posix shell understands it, bash included.

> Things to consider: How likely is TMOUT to be exported in bash (causing a 
> false 
> positive), vs. BASH_VERSION to be exported in ksh (which causes way more 
> problems than a spurious export of TMOUT)?  On the other hand, using a 
> positive 
> test (TMOUT being set) vs. a negative test (BASH_VERSION is not set) means 
> that 
> your version avoids 2 forks on ash or Solaris /bin/sh while mine does not.  
> Should we document $TMOUT as a reliable way to detect ksh, the way we already 
> use {BASH,ZSH}_VERSION as reliable witnesses of those two shells?

Where did you get the idea that TMOUT is a reliable way to detect ksh?
And since when are 2 forks a suitable tradeoff for portability?

Thanks,
Ralf