Claudius Hubig wrote: > bash(1) does not appear to mention $@. It does but unfortunately it mentions it as a variable named @ and not as $@ making it difficult to search. This problem has been discussed upstream for instance here:
http://lists.gnu.org/archive/html/bug-bash/2011-12/msg00097.html Maybe one day it will have a $@ together so that it can be found easier. I know I voted to include it. The documentation lists them like this: The special parameters * and @ have special meaning when in double quotes (see PARAMETERS below). ... Special Parameters The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed. * Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, it expands to a single word with the value of each parameter separated by the first character of the IFS special variable. That is, "$*" is equivalent to "$1c$2c...", where c is the first character of the value of the IFS variable. If IFS is unset, the parameters are separated by spaces. If IFS is null, the parameters are joined without intervening separators. @ Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter expands to a separate word. That is, "$@" is equivalent to "$1" "$2" ... If the double-quoted expansion occurs within a word, the expansion of the first parameter is joined with the beginning part of the original word, and the expansion of the last parameter is joined with the last part of the original word. When there are no positional parameters, "$@" and $@ expand to nothing (i.e., they are removed). So in general if you want to pass arguements through then you want to always use "$@". If you want all of the arguments to be part of one single string then use "$*". Always using one of the quoted forms is almost always better than using the unquoted form. When unquoted the $* and $@ are equivelent. Historical trivia: In the Bourne shell "$@" was documented to be the same as "" if there weren't any arguments. In hindsight that was undesirable since it was almost never what was wanted. It just fell out of the normal use of quoting on a variable. If you said "$foo" and foo was empty then you also got an empty "" string. So the same thing happened for "$@". But "$@" was already special and an empty string there is not a useful behavior. It required ${1+"$@"} to be used to get the desired behavior. ${parameter+word} Use Alternate Value. If parameter is unset, nothing is substituted, otherwise the expansion of word is substituted. That idiom ${1+"$@"} was often seen in scripts meaning that if $1 was set then replace the combination (due to the + action) with "$@". If $1 was empty then it avoided getting an empty string. If $1 had something in it then "$@" was guarenteed not to be the empty string. All modern shells have the new behavior. But this isn't so historical. To be portable to Sun's /bin/sh that idiom is still needed. And so if you ever see programs designed to be portable to those systems that idiom is still useful to know about. Bob
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