A bash script to raise a macOS notification or alert with no dependencies. Save this file as `notify` and then symlink it to `alert`.

notify.sh

#!/usr/bin/env bash
#
# Quinn Comendant <[email protected]>
# 11 Jul 2020 11:18:13

set -o pipefail;
set -o errexit;
set -o nounset;
set -o noclobber;

scriptname=$(basename "$0");

#
# Functions
#

function _usage() {
    echo "Usage: $scriptname [OPTIONS] [< STDIN]

Raise a macOS notification using AppleScript.

OPTIONS

    -m MESSAGE      The notification message (required if not using STDIN).
    -s SUBTITLE     A notification subtitle.
    -S              Play a notification sound.
    -t TITLE        A notification title.

";
    exit 1;
}

function _error() {
    local IFS='';
    echo -e "$*" 1>&2
    exit 1;
}

function _notify() {
    export notify_message notify_subtitle notify_title notify_sound;
    if [[ -n $notify_sound ]]; then
        osascript -e 'display notification (system attribute "notify_message") with title (system attribute "notify_title") subtitle (system attribute "notify_subtitle") sound name (system attribute "notify_sound")' >/dev/null &
        # osascript -e 'tell application "Finder"' -e 'activate' -e 'display notification (system attribute "notify_message") with title (system attribute "notify_title") subtitle (system attribute "notify_subtitle") sound name (system attribute "notify_sound")' -e 'end tell' &
    else
        osascript -e 'display notification (system attribute "notify_message") with title (system attribute "notify_title") subtitle (system attribute "notify_subtitle")' >/dev/null &
        # osascript -e 'tell application "Finder"' -e 'activate' -e 'display notification (system attribute "notify_message") with title (system attribute "notify_title") subtitle (system attribute "notify_subtitle")' -e 'end tell' &
    fi
}

function _alert() {
    if [[ -n $notify_subtitle ]]; then
        notify_title="${notify_title} (${notify_subtitle})";
    fi
    export notify_message notify_title notify_sound;
    osascript -e 'display alert (system attribute "notify_title") message (system attribute "notify_message") as critical buttons {"OK"} default button "OK"' >/dev/null &
    # osascript -e 'tell application "Finder"' -e 'activate' -e 'display alert (system attribute "notify_title") message (system attribute "notify_message") as critical buttons {"OK"} default button "OK"' -e 'end tell' >/dev/null &

    if [[ -n $notify_sound ]]; then
        sleep 1 && afplay /System/Library/Sounds/Pop.aiff &>/dev/null &
    fi
}

function _iconv() {
    local str;
    read -rd '' str;
    iconv -f UTF8 -t MACROMAN//IGNORE <<<"$str" 2>/dev/null || true;
}


#
# Main
#

# Look at stdin for the message (`-t 0` tests if input is not a tty, i.e., stdin exists via pipe).
notify_message=;
if [[ ! -t 0 ]]; then
    notify_message=$(_iconv);
fi

# Display help if run without arguments.
[[ $# == 0 && -z $notify_message ]] && _usage 1>&2

# Process command line options.
notify_subtitle='';
notify_title='Terminal';
notify_sound='';
while getopts 'hm:s:St:-:' opt ; do
    case $opt in
        (h) _usage;;
        (m) if [[ -n $notify_message ]]; then
                _error "Message provided via -m and stdin; choose one and try again.";
            fi
            notify_message=$(_iconv <<<"$OPTARG");;
        (t) notify_title=$(_iconv <<<"$OPTARG");;
        (s) notify_subtitle=$(_iconv <<<"$OPTARG");;
        (S) notify_sound='Pop';;
        (-) case $OPTARG in
            (help) _usage;;
            (?) _error "Invalid option: '$OPTARG'. Run with -h for help.";;
        esac ;;
        (?) _error "Invalid option: '$opt'. Run with -h for help.";;
        (*) _error "An unexpected error occurred.";;
    esac
done

# Remove options.
shift $((OPTIND - 1))

[[ -z $notify_message ]] && _error "No message provided. Run with -h for help.";

type -P osascript >/dev/null || _error "The osascript command is not available";

case $scriptname in
    (notify) _notify;;
    (alert) _alert;;
esac
unset -v notify_message notify_subtitle notify_title notify_sound;