posix-arrays-a-mini.sh

#!/bin/sh
# shellcheck disable=SC2154,SC2086

# Copyright: friendly bits
# github.com/friendly-bits

# posix-arrays-a-mini.sh

# emulates associative arrays in POSIX shell

# NOTE: this is a stripped down to a minimum and optimized for very small arrays version,
# which includes a minimal subset of functions from the main project:
# https://github.com/friendly-bits/POSIX-arrays


# get keys from an associative array
# whitespace-delimited output is set as a value of a global variable
# 1 - array name
# 2 - var name for output
get_a_arr_keys() {
	___me="get_a_arr_keys"
	case $# in 2) ;; *) wrongargs "$@"; return 1; esac
	_arr_name="$1"; _out_var="$2"
	_check_vars _arr_name _out_var || return 1

	eval "$_out_var=\"\$(printf '%s ' \${_a_${_arr_name}___keys:-})\""

	:
}

# 1 - array name
# 2 - 'key=value' pair
set_a_arr_el() {
	___me="set_a_arr_el"
	case $# in 2) ;; *) wrongargs "$@"; return 1; esac
	_arr_name="$1"; ___pair="$2"
	case "$___pair" in *=* ) ;; *) printf '%s\n' "$___me: Error: '$___pair' is not a 'key=value' pair." >&2; return 1; esac
	___key="${___pair%%=*}"
	___new_val="${___pair#*=}"
	_check_vars _arr_name ___key || return 1

	eval "___keys=\"\${_a_${_arr_name}___keys:-}\"
			_a_${_arr_name}_${___key}"='${___new_val}'

	case "$___keys" in
		*"$_nl$___key"|*"$_nl$___key$_nl"* ) ;;
		*) eval "_a_${_arr_name}___keys=\"$___keys$_nl$___key\""
	esac

	:
}

# 1 - array name
# 2 - key
# 3 - var name for output
get_a_arr_val() {
	___me="get_a_arr_val"
	case $# in 3) ;; *) wrongargs "$@"; return 1; esac
	_arr_name="$1"; ___key="$2"; _out_var="$3"
	_check_vars _arr_name ___key _out_var || return 1
	eval "$_out_var=\"\$_a_${_arr_name}_${___key}\""
}


## Backend functions

_check_vars() {
	case "${nocheckvars:-}" in *?*) return 0; esac
	for ___var in "$@"; do
		eval "_var_val=\"\$$___var\""
		case "$_var_val" in ''|*[!A-Za-z0-9_]* )
			case "$___var" in
				___key) _var_desc="key" ;;
				_arr_name) _var_desc="array name" ;;
				_out_var) _var_desc="output variable name"
			esac
			printf '%s\n' "$___me: Error: invalid $_var_desc '$_var_val'." >&2
			return 1
		esac
	done
}

wrongargs() {
	echo "$___me: Error: '$*': wrong number of arguments '$#'." >&2
}

set -f
export LC_ALL=C
_nl='
'