temp.sh

temp.sh

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

# MIT license (c) 2021 https://github.com/slowpeek
# Homepage: https://gist.github.com/slowpeek/f3e851f5c6fa6a7ba1f33d1e903bf4a9

# Temporarily assign a new value to a var and restore it
# later. Strings only. The code is simple on intention, use it
# correctly.
#
#     temp var new_value        # old=$var; var=new_value
#     do_something
#     temp var                  # var=$old; unset old

temp () {
    # Flaw: it is not correct in case of declared but not set vars
    # like 'declare x'. On restore such var would become set with an
    # empty value.

    [[ $1 == var ]] || local -n var=$1
    local -n old=TE__$1

    if (($# > 1)); then
        ! declare -p var &>/dev/null || old=${var-}
        var=$2
    else
        if [[ -v old ]]; then
            var=$old
            unset -v old
        else
            unset -v var
        fi
    fi
}