rc/sh/maybesudo

#!/usr/bin/env sh
# YES_ZSH
# YES_BASH
# YES_DASH
# YES_ASH

maybesudo_() { ### @-
    ### mimic certain features of `sudo` for systems without it installed.
    ### as it stands, this mostly just handles some environment variables.
    ###
    ### try this: `maybesudo_ -u "$USER" printenv`
    # TODO: you know, awk has an ENVIRON array that might be easier to work with.
    local name=
    local env_cleanup=0
    while getopts :AEHKPSVbhiklnsvC:U:g:p:r:t:u: name; do
        case $name in
        K|V|k)
        # K: sure kill
        # V: version
        # k: kill
            note 'maybesudo: your system does not have sudo installed!'
            return 0
            ;;

        h)
            printf "%s\n" 'maybesudo - a dumb utility for systems without sudo'
            printf "\n"
            printf "%s\n" 'usage: maybesudo -h | -V'
            printf "%s\n" 'usage: maybesudo [command]'
            return 0
            ;;

        A|E|H|P|S|n|p)
        # A: askpass
        # E: preserve environment
        # H: HOME
        # P: preserve group vector
        # S: stdin (password)
        # n: non-interactive
        # p: prompt
            note 'maybesudo: option has no effect --' "'$name'"
            ;;

        C|U|b|g|i|l|r|s|t)
        # C: close from (fd)
        # U: other user (in conjunction wiht -l)
        # b: background
        # g: group
        # i: simulate initial login (TODO)
        # l: list
        # r: role (SELinux)
        # s: shell (TODO)
        # t: type (SELinux)
            note "maybesudo: unsupported option --" "'$name'"
            return 1
            ;;

        u)      # user
            if [ -z "$USER" -o "$OPTARG" != "$USER" ]; then
                note 'maybesudo: users other than yourself are unsupported!'
                return 1
            fi
            env_cleanup=1
            ;;

        :)
            note 'maybesudo: option requires an argument --' "'$OPTARG'"
            return 1
            ;;
        default)
            note 'maybesudo: invalid option --' "'$OPTARG'"
            return 1
            ;;
        esac
    done

    shift $((OPTIND-1))

    if [ "$env_cleanup" = 1 ]; then
        (
            # portably listing exported variable names is virtually impossible
            # without the blessing of null-terminated strings, so don't even try.
            # just export the bare minimum that a fairly stock sudo would.

            # $path is special in zsh, so call it pathy instead.
            local \
                colors= display= dpkg_colors= home= hostname= krb5ccname= \
                ls_colors= pathy= ps1= ps2= user= username= xauthority= \
                xauthorization=

            [ -z "$COLORS" ] || colors=COLORS="$COLORS"
            [ -z "$DISPLAY" ] || display=DISPLAY="$DISPLAY"
            [ -z "$DPKG_COLORS" ] || dpkg_colors=DPKG_COLORS="$DPKG_COLORS"
            [ -z "$HOME" ] || home=HOME="$HOME"
            [ -z "$HOSTNAME" ] || hostname=HOSTNAME="$HOSTNAME"
            [ -z "$KRB5CCNAME" ] || krb5ccname=KRB5CCNAME="$KRB5CCNAME"
            [ -z "$LS_COLORS" ] || ls_colors=LS_COLORS="$LS_COLORS"
            [ -z "$PATH" ] || pathy=PATH="$PATH"
            [ -z "$PS1" ] || ps1=PS1="$PS1"
            [ -z "$PS2" ] || ps2=PS2="$PS2"
            [ -z "$USER" ] || user=USER="$USER"
            [ -z "$USERNAME" ] || username=USERNAME="$USERNAME"
            [ -z "$XAUTHORITY" ] || xauthority=XAUTHORITY="$XAUTHORITY"
            [ -z "$XAUTHORIZATION" ] || xauthorization=XAUTHORIZATION="$XAUTHORIZATION"

            # don't eat up precious command space with dumb colors.
            # xargs --show-limits says:
            # Maximum length of command we could actually use: 5080
            [ "${#ls_colors}" -le 1024 ] || ls_colors==

            # sudo also sets SUDO_COMMAND, SUDO_GID, SUDO_UID, SUDO_USER, and MAIL,
            # but who needs those?

            # env seems to treat arguments of "=" as a no-op across GNU and busybox.
            env -i \
                "${colors:-=}" \
                "${display:-=}" \
                "${dpkg_colors:-=}" \
                "${home:-=}" \
                "${hostname:-=}" \
                "${krb5ccname:-=}" \
                "${ls_colors:-=}" \
                "${pathy:-=}" \
                "${ps1:-=}" \
                "${ps2:-=}" \
                "${user:-=}" \
                "${username:-=}" \
                "${xauthority:-=}" \
                "${xauthorization:-=}" \
                "$@"
        )

    else
        # run it in a subshell so it won't affect ours.
        # TODO: run through env anyway for consistency.
        #       (`maybesudo export` should fail)
        ( "$@"; )
    fi

    # don't put any code here or you'll clobber $?.
}

[ -n "${preload+-}" ] || maybesudo_ "$@"