TITLE: Bash script to download audio from Youtube
DATE: 2024-06-26
AUTHOR: John L. Godlee
====================================================================


This post is actually about a trick I learned that allows bash 
scripts to accept input either as a string or from stdin.

Here is the code. It first checks whether at least one argument is 
provided to the script. If an argument is found it creates a 
variable containing all the arguments. If no arguments are found, 
then it waits for input from stdin, which can either come from a 
pipe or can be typed in after the script is called.

    #!/usr/bin/env bash

    # If argument provided
    if [ $# -gt 0 ]; then
        input="$*"
    else
        # Read from stdin 
        while IFS= read -r line; do
            input+="$line"
        done
    fi

    echo $input

I used this trick to write a script to download audio files from 
Youtube using yt-dlp. I wanted to be able to integrate the script 
with ytfzf, which can search Youtube from the terminal using FZF 
and optionally print the URL of the selected video.

  [yt-dlp]: https://github.com/yt-dlp/yt-dlp
  [ytfzf]: https://ytfzf.github.io/

    #!/usr/bin/env sh

    # Download audio only using yt-dlp

    # If argument provided
    if [ $# -gt 0 ]; then
        input="$*"
    else
        # Read from stdin 
        while IFS= read -r line; do
            input+="$line"
        done
    fi

    # Download 
    yt-dlp \
        -f bestaudio \
        --extract-audio \
        --audio-format m4a \
        -S +size,+br \
        -o "$PWD/%(title)s.%(ext)s" \
        --external-downloader aria2c \
        --external-downloader-args "-x 5 -s 5 -j 5 -c -k 1M" $input

The script can be called in various ways.

Passing an argument:

    yt_audio https://www.youtube.com/watch?v=Atkp8mklOh0

Using stdin:

    echo "https://www.youtube.com/watch?v=Atkp8mklOh0" | yt_audio

Using stdin with ytfzf:

    ytfzf -L Terry Barentsen Hotline Cooper Ray | yt_audio

With multiple URLs as arguments:

    yt_audio https://www.youtube.com/watch?v=WyV894c8oqI 
https://www.youtube.com/watch?v=Atkp8mklOh0

With multiple URLs from stdin:

    echo "https://www.youtube.com/watch?v=WyV894c8oqI 
https://www.youtube.com/watch?v=Atkp8mklOh0" | yt_audio