Hi June,
* June Fang wrote on Fri, Feb 24, 2006 at 04:43:03PM CET:
> On 2/24/06, June Fang <[EMAIL PROTECTED]> wrote:
> >
> > i know ${ZSH_VERSION} means variable substituting;
> > and ${ZSH_VERSION:+set} means "If parameter is null or unset, nothing
> > ~~ Note the `:`
> > is substituted, otherwise the expansion of word is substituted."
> > ---- from Bash reference manual
> >
> > but what dose ${ZSH_VERSION+set} without the `:` means ?
It substitutes `set' when the variable is set; i.e., ZSH_VERSION may
also be empty. This is done because some older shells do not understand
${foo:+bar} ${foo:-bar} ${foo:=bar}
correctly, but only
${foo+bar} ${foo-bar} ${foo=bar}
This actually quite inconvenient: there are also older shells that do
not support `unset'. I think that's one reason why the config.cache
precious variables come in pairs:
ac_cv_env_CC_set=
ac_cv_env_CC_value=
The first one is a witness as to whether CC was set or not.
> and what's more, the entire lines:
> 15 if test -n "${ZSH_VERSION+set}" && (emulate sh) >/dev/null 2>&1;
> then
> 16 emulate sh
> i guess it means execuate "emulate sh" in subshell, and
> if it success, do it in our current shell ? am i right ?
Yes. `emulate sh' is necessary for zsh to behave correctly. zsh is the
default /bin/sh on some systems.
Cheers,
Ralf
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