Add to array only within scope of function

Question

I'm writing a function that will make a REST API calls which could be either GET, PUT, DELETE, POST, etc.

I would like to feed this method to the function as a parameter and add it to the options array for that single function call. Is this possible?

Currently I am solving this by creating a separate local array but would prefer to only use the single options array.

#!/bin/bash

options=(
    --user me:some-token
    -H "Accept: application/json"
)

some_func () {
    local urn=$1
    shift
    local func_opts=("${options[@]}" "$@")
    printf '%s\n' "${func_opts[@]}"
}

# This should return all options including -X GET
some_func /test -X GET

# This should return only the original options
printf '%s\n' "${options[@]}"

I could also use a temporary array to store the contents of options, add the new options, and then reset it before the function ends, but I don't think that is a particularly clean method either.

Stéphane Chazelas · Accepted Answer · 2019-02-08 22:12:39Z

With bash 5.0 and above, you can use the localvar_inherit option which causes local to behave like in ash-based shells, that is where local var makes the variable local without changing its value or attributes:

shopt -s localvar_inherit
options=(
  --user me:some-token
  -H "Accept: application/json"
)
some_func () {
  local urn=$1
  shift
  local options # make it local, does not change the type nor value
  options+=("$@")
  printf '%s\n' "${options[@]}"
}

some_func /test -X GET

With any version, you can also do:

some_func () {
  local urn=$1
  shift
  eval "$(typeset -p options)" # make a local copy of the outer scope's variable
  options+=("$@")
  printf '%s\n' "${options[@]}"
}

Jeff Schaller · Accepted Answer · 2019-02-08 20:54:07Z

4

One option would be to explicitly use a subshell for the function, then override its local copy of the array, knowing that once the subshell exits, the original variable is unchanged:

# a subshell in () instead of the common {}, in order to munge a local copy of "options"
some_func () (
    local urn=$1
    shift
    options+=("$@")
    printf '%s\n' "${options[@]}"
)

answered Feb 8, 2019 at 20:54

Jeff Schaller♦

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