On Sat, Aug 17, 2024 at 12:41:45 +0200, Freek de Kruijf wrote:
> Apparently I have a problem with the concept of $@, I see it as list of zero
> or more non-whitespaced elements, and quotes around it makes it into a single
> element. Like a parameter p with a content of zero or more non-whitespaced
> elements, where the quotes make in into a single element.
>
> Thanks for teaching me this concept. It must have some meaning in more
> complicated situations.
In a nutshell:
"$*" All of the parameters joined together with spaces between them.
"$@" All of the parameters expanded as a list of zero or more words.
$* Usually a bug.
$@ Usually a bug.
The unquoted forms undergo THREE rounds of expansion. First, each
parameter is expanded as a separate word, like "$@" does. Then, each
of those words undergoes word splitting using IFS, to generate a second
list of words. Finally, each of those words undergoes filename expansion
(globbing) to generate a third list of words. The final result is that
third list.
You almost never want that.
Here's an illustration of how they work:
hobbit:~$ set -- "a b" "" "files matching foo.p*"
hobbit:~$ printf '<%s> ' "$*" ; echo
<a b files matching foo.p*>
hobbit:~$ printf '<%s> ' "$@" ; echo
<a b> <> <files matching foo.p*>
hobbit:~$ printf '<%s> ' $* ; echo
<a> <b> <files> <matching> <foo.pdf> <foo.pl> <foo.png>
hobbit:~$ printf '<%s> ' $@ ; echo
<a> <b> <files> <matching> <foo.pdf> <foo.pl> <foo.png>
As documented, "$*" gives one big string, "$@" gives a list of strings,
and the unquoted forms give... that.
