A script to play a youtube video or its audio alone in mpv.

ytmp.sh

#!/bin/sh
# vim:sw=4:ts=4:et
################################################################################
#                                                                              #
# A shell script which searches youtube for a video or audio                   #
# and plays it in mpv.                                                         #
# Created by Supershadoe                                                       #
#                                                                              #
################################################################################

# Test for dependencies #
for cmd in {ffmpeg,youtube-dl,mpv}; do
    if ! command -v $cmd > /dev/null 2>&1; then
        echo "$cmd is not installed."
        exit 1
    fi
done

# copying argument to variable for use #
arg2=$2

# Functions for different actions #
usage() {
    cat << EOF >&2
A shell script to search youtube for a video or audio and play it in mpv.
Created by Supershadoe <<https://github.com/supershadoe>>

SYNTAX: ytmp [-- | { -l|--link } | { -s | --search } | { -h | --help }]
             [link|search term] [-nv]

USAGE:
    -h, --help      shows this help message and exits
    -s, --search    searches youtube for the string given in arguments
    -l, --link      opens youtube link in mpv

    -nv             no video(only audio mode)
Flags other than these throws an error and exits.
The no video flag is optional and by default video is played.
Extra arguments are also ignored.
If you want the script to detect the mode and run(instead of providing mode
manually), give -- before typing your link/search term.
EOF
}

link() {
    title=$(youtube-dl --get-title "$arg2")
    [ $? -eq 0 ] && {
        echo "Playing..."
        echo -e "\nFile name: $title"
        mpv $no_video_arg --ytdl-raw-options=write-sub=,write-auto-sub=,sub-lang=en "$arg2"
        unset title
        unset arg2
        echo "Bye!!"
    }
}

search() {
    numres=5
    startres=1
    ctl_sch="y"
    while [ "$ctl_sch" = "y" -o -z "$ctl_sch" ]; do
        youtube-dl --get-title --playlist-start $startres "ytsearch$numres:$arg2"
        read -p "Which video?(1-5,0 for none) " choice
        if [ $choice -lt 6 ] && [ $choice -gt 0 ]; then
            itemnum=$(( choice + (numres - 5) ))
            title=$(youtube-dl --get-title --playlist-item $itemnum "ytsearch$numres:$arg2")
            ctl_sch="n"
        elif [ $choice -eq 0 ]; then
            read -p "Show more results? [Y/n]: " ctl_more
            if [ "$ctl_more" = "n" ]; then
                exit 1
            fi
        else
            echo "Choice invalid..."
            exit 1
        fi
    done
    unset startres
    unset ctl_sch
    unset choice
    unset ctl_more
    echo "Playing..."
    echo -e "\nFile name: $title"
    mpv $no_video_arg --ytdl-raw-options=write-sub=,write-auto-sub=,sub-lang=en,playlist-item=$itemnum "ytdl://ytsearch$numres:$arg2"
    unset title
    unset itemnum
    unset numres
    unset arg2
    echo "Bye!!"
}

unsetvariables() {
    unset numres
    unset startres
    unset ctl_sch
    unset choice
    unset itemnum
    unset ctl_more
}

# main #
[ "$3" = "-nv" ] && no_video_arg="--no-video --force-window=no"
case "$1" in
    -l | --link)
        link
        [ $? -ne 0 ] && echo "Can't open link..." && exit 1;;
    -s | --search)
        search;;
    -h | --help)
        usage;;
    --)
        link 2> /dev/null || search
        ;;
    "")
        echo "No option given..."
        usage
        exit 1;;
    *)
        echo "Invalid choice..."
        usage
        exit 1;;
esac

Dependencies: ffmpeg, mpv and youtube-dl
Save this script to some folder which is in your PATH variable (/usr/local/bin or some custom folder)
Refer this page to see how to add custom folders to PATH variable in zsh(I think it works for bash also except that you need to add those lines in .bashenv file instead of .zshenv)