stack.sh

stack.sh

# -*- mode: sh; sh-shell: bash; -*-
# shellcheck shell=bash

# MIT license (c) 2021 https://github.com/slowpeek
# Homepage: https://gist.github.com/slowpeek/3310c2f09b80d0b2e175122e8c8cae64

# bye.sh https://gist.github.com/slowpeek/6127166369d8abd230c30c20cc6a9152

# Simple stack for strings. It operates on var names:
#
#     push <var>*
#     pop <var>*
#
# 'push' and 'pop' operate on the default stack. 'push_n' and 'pop_n'
# operate on a named stack, the name is passed as the first arg. Names
# are case-insensitive.
#
# If a variable doesnt exist when popping, it would be created as a
# global one.
#
# EXAMPLES
#
# Temporarily change IFS value:
#
#     a=(1 2 3)
#     push IFS
#     IFS=:
#     echo "${a[*]}"
#     pop IFS
#
# Swap values using a named stack (no reason to use a named stack
# instead of the default one here though):
#
#     a=12 b=44
#     push_n my1 a b
#     pop_n my1 a b

_ () {
    unset -f _

    declare -g -a ST__STACK=()   # Default stack.
    declare -g -A ST__NAMED=()   # Named stacks registry.
}; _

push () {
    while (($# > 0)); do
        [[ -v "$1" ]] || bye "Variable ${1@Q} is not set."
        ST__STACK+=("${!1}")
        shift
    done
}

pop () {
    while (($# > 0)); do
        if [[ ! -v ST__STACK ]]; then
            [[ ${ST__POP_EXIT-} == n ]] || bye 'The stack is empty.'
            return 1
        fi

        if [[ $1 == var ]]; then
            var=${ST__STACK[-1]}
            unset -v 'ST__STACK[-1]'
        else
            local -n var=$1

            # shellcheck disable=SC2034
            var=${ST__STACK[-1]}
            unset -v 'ST__STACK[-1]'

            unset -n var
        fi

        shift
    done
}

push_n () {
    local st__name=${1^^}
    shift

    local -n ST__STACK=ST__STACK_$st__name

    if [[ ! -v ST__NAMED["$st__name"] ]]; then
        # shellcheck disable=SC2034
        ST__NAMED[$st__name]=t
        declare -g -a ST__STACK_"$st__name"
        ST__STACK=()
    fi

    push "$@"
}

pop_n () {
    local st__name=${1^^}
    shift

    # shellcheck disable=SC2178
    local -n ST__STACK=ST__STACK_"$st__name"

    ST__POP_EXIT=n pop "$@" || bye "${st__name@Q} named stack is empty."
}