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configure script question ?


From: June Fang
Subject: configure script question ?
Date: Fri, 24 Feb 2006 23:26:38 +0800

sorry in advance if stupid question, but i am a really new bie.

i found the following shell script in the configure file of autoconf-2.59
but dose that means ?
     15  if test -n "${ZSH_VERSION+set}" && (emulate sh) >/dev/null 2>&1; then
     16   emulate sh
     17   NULLCMD=:
     18   # Zsh 3.x and 4.x performs word splitting on ${1+"$@"}, which
     19   # is contrary to our usage.  Disable this feature.
     20   alias -g '${1+"$@"}'='"$@"'
     21 elif test -n "${BASH_VERSION+set}" && (set -o posix)
>/dev/null 2>&1; then
     22   set -o posix
     23 fi

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 ?

thanks in advance.




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