2

If getopts is a bash function, by my understanding, you need to pass $@ - the whole arguments to getopts to let the function know what kind of arguments you have in order to proceed, right?

It seems to me that you don't need it, so how the getopts get to know what arguments I have in the current scope? Does it have a way to trace the previous call like the other high-level languages do?

while getopts abcde opt; do
              ˄˄˄˄˄ <-- you only need to pass the argument labels here, 
                        how getopts knows what arguments I have
    case $opt in
        ...
    esac
done
Jeff Schaller
  • 67,283
  • 35
  • 116
  • 255
Till
  • 193
  • shift and set (well and ., eval (well and command when called as command shift/eval...)) are other shell builtins that can access/modify positional parameters. read, readarray, typeset, unset, [, printf are examples of shell builtins which like getopts can access/modify shell variables. – Stéphane Chazelas Nov 21 '23 at 14:41

1 Answers1

4

getopts is a shell built-in, so it can reference $@ directly. It also sets the shell variables OPTARG and OPTIND. (Note that inside a function, getopts will reference that function's $@ rather than the global arguments. You should localise OPTIND if you want a repeatable (odempotent) function call.)

The synopsis (summary) is

getopts optstring name [arg ...]

and the description is such that,

getopts is used by shell procedures to parse positional parameters. optstring contains the option characters to be recognized; if a character is followed by a colon, the option is expected to have an argument, which should be separated from it by white space.

Note that (at least) the bash documentation (man bash) also notes,

getopts normally parses the positional parameters, but if more arguments are supplied as arg values, getopts parses those instead.

References

Chris Davies
  • 116,213
  • 16
  • 160
  • 287
  • If its passible for us to write a function which can reference $@ directly??? – Till Nov 21 '23 at 08:16
  • @Till of course. printf '%s\n' "$@" references $@ directly, for example – Chris Davies Nov 21 '23 at 08:18
  • umm, i dont geit it. If I do printf '%s\n' "$@" in function Foo, it wont display the $@ which where called Foo but only display whatever passed to Foo – Till Nov 21 '23 at 08:23
  • Yes that's right. Ask a new question about referencing the global $@ in a function and let me know, and I'll answer it there for you. Or someone else might – Chris Davies Nov 21 '23 at 08:24
  • sure! I will do it, but it limits one post in every 40 mins, I will post you a link later, thank you very much! – Till Nov 21 '23 at 08:29
  • 1
    https://unix.stackexchange.com/questions/761988/how-to-referencing-without-pass-it-in-bash-function Thank you for your help! – Till Nov 21 '23 at 09:00