I like to think "$@" as keyword because it only works with that exact incantation. For example "-v $@" won’t work as it will be expanded to a single argument instead of a list of arguments.
$* is not really useful in itself but can be used to indicate intent that no argument expansion should happen.
Yes, "$@" is the only thing I use and it’s a confusing syntax. Because "" usually means “don’t split” or “give me one string”, but "$@" gives you multiple strings, in contrast to “$*”. (And the other two possibilities are even more confusing.)
It generalizes to arrays – you should use "${array[@]}" and not "${array[*]}". I’ve never found any reason to use the latter or any other variant:
In Oil, you can just write @myarray instead of "${myarray[@]}". And @ARGV is an alias for "$@". Let me know if it doesn’t make sense :)
oil$ var myarray = @('has spaces' foo)
oil$ var s = $'has\ttabs'
oil$ echo $s
has tabs
oil$ lines() { for x in @ARGV; do echo $x; done }
oil$ lines @myarray $s
has spaces
foo
has tabs
So the hilarious thing is that POSIX shell rules are even more complicated than what I laid out in that post. I’ve been meaning to write a followup Shell Has Context-Sensitive Evaluation to explain this.
But it’s buried here under the bit about EvalWordToString and EvalWordSequence:
So you can simply use "${array[@]}" in all those cases because it’s on the RHS of an assignment. But yeah if you want to use * for “clarity”, I won’t argue. It’s a matter of style. Shell syntax has nothing to do with its semantics :)
Please don’t. This is a gotcha question about esoterica around bash. It doesn’t tell you much about the candidate other than if they read the right set of blog articles or experienced a particular kind of issue in the past.
A better question would be “What quirks have most surprised you in bash?” Or something similar. It doesn’t assume any particular piece of trivia and a great candidate might even teach you something you didn’t know.
This says Bash, but isnt that POSIX sh?
Yes, but Bash is compatible with POSIX sh and the author may not have known that the script was only using POSIX sh features.
I like to think
"$@"as keyword because it only works with that exact incantation. For example"-v $@"won’t work as it will be expanded to a single argument instead of a list of arguments.$*is not really useful in itself but can be used to indicate intent that no argument expansion should happen.For example:
NOTE: this also works with bash arrays
A counter-point to the bernstein-chaining style is
"${*@Q}"Sometimes some programs want to get the command as a string and this incantation allow you to escape the array properly back into bash.
Eg:
It seems to work the same way with @ for me. As rule I never use anything like
$*– it’s just easier to remember that way.(note: it doesn’t work at all in bash 4.3)
yeah makes sense. those poor macOS users with their bash 3.0 are missing out on the good things.
Yes,
"$@"is the only thing I use and it’s a confusing syntax. Because""usually means “don’t split” or “give me one string”, but"$@"gives you multiple strings, in contrast to “$*”. (And the other two possibilities are even more confusing.)It generalizes to arrays – you should use
"${array[@]}"and not"${array[*]}". I’ve never found any reason to use the latter or any other variant:See Thirteen Incorrect Ways and Two Awkward Ways to Use Arrays
In Oil, you can just write
@myarrayinstead of"${myarray[@]}". And@ARGVis an alias for"$@". Let me know if it doesn’t make sense :)In Neovim we’re using it to:
shellcheck doesn’t complain about this, but maybe there’s a better way? :)
So the hilarious thing is that POSIX shell rules are even more complicated than what I laid out in that post. I’ve been meaning to write a followup Shell Has Context-Sensitive Evaluation to explain this.
But it’s buried here under the bit about
EvalWordToStringandEvalWordSequence:https://github.com/oilshell/oil/wiki/Shell-WTFs
So you can simply use
"${array[@]}"in all those cases because it’s on the RHS of an assignment. But yeah if you want to use*for “clarity”, I won’t argue. It’s a matter of style. Shell syntax has nothing to do with its semantics :)Nice. I see this as an interview question sometimes.
Please don’t. This is a gotcha question about esoterica around bash. It doesn’t tell you much about the candidate other than if they read the right set of blog articles or experienced a particular kind of issue in the past.
A better question would be “What quirks have most surprised you in bash?” Or something similar. It doesn’t assume any particular piece of trivia and a great candidate might even teach you something you didn’t know.
I’ve seen it, not used it :)
Ah, I completely misread your comment. Sorry about that.