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.
#!/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