Becoming commands in Bash folders

I want to show my focus on execute commands in Bash using watchers and folders. I have named this trick Bash Folders.

I have a problem. I needed to run a lot of commands on files. For example, every day I need to transform videos (the extension isn't relevant) to MP4. Ok.

Classic steps to follow:

Open the terminal.
Change the directory.
Run ffmpeg (At the reality, I used an alias).
Wait for it to finish.
Move output to the target folder.

Sound familiar? Now, you think repeating all steps hundreds of times a day. It's crazy!

My solution

It's easy. If a new video is copied in a specific folder, then run a command using this file.

inotifywait is a unix tool that checks for updates in folders. The following code runs ffmpeg if a new file is created or moved in my-folder-to-watch.

inotifywait -m -e create,moved_to --format '%f' my-folder-to-watch |
while read -r filename; do
    ffmpeg -i $filename ...
done

Do you want to filtering files by extension? Use --includei flag.

EXTENSIONS_TO_WATCH="mkv|mp4|avi|mov"

inotifywait -m -e create,moved_to my-folder-to-watch \
--includei "\.($EXTENSIONS_TO_WATCH)$" --format '%f' |
while read -r filename; do
    ffmpeg -i $filename ...
done

If you're looking for a code that is more flexible, but more verbose, you can use a loop with a conditional statement to check the extension.

EXTENSIONS_TO_WATCH=("mkv" "mp4" "avi" "mov")
inotifywait -m -e create,moved_to my-folder-to-watch --format '%f' |
while read -r filename; do
    extension="${filename##*.}"
    for ext in "${EXTENSIONS_TO_WATCH[@]}"; do
        if [[ "$ext" = "$extension" ]]; then
            ffmpeg -i $filename ...
        fi
    done
done

Now my steps are:

Copy, or move, file to specific folder.
Wait for it to finish.
Move the output to the target folder.

But... How do I know if ffmpeg is finished? You can achieve this by sending desktop notifications (notify-send) or by creating a temporal plain file (optimizing_please_wait).

Example

This script implements everything we discussed.

Create a file, possibly named bash-folders-video-optimizer, and copy the following contents:

#!/usr/bin/env bash

# --
# Description: Script that watches when new videos are added to a folder and optimizes them.
# --
# Requirements: Install inotify-tools and ffmpeg
# Example Debian: $sudo apt install ffmpeg
# --
# Cron: @reboot bash-folders-video-optimizer.sh >/dev/null 2>&1 &
# --

# START
set -e

# VARIABLES
PROGNAME=$(basename "$0")
FOLDER_ORIGIN="$2"
EXTENSIONS_TO_WATCH=("mkv" "mp4" "avi" "mov")
MESSAGE_WAITING="optimizing_please_wait"

# FUNCTIONS

usage() {
    if [ "$*" != "" ] ; then
        echo "Error: $*"
    fi

    cat << EOF
Usage: $PROGNAME [OPTION]
Watches when new videos are added to a folder and optimizes them.
Options:
--folder [path]  Folder path where new video will be monitored and optimized
--help           Display this usage message and exit
EOF

    exit 1
}

start() {
    # Monitors the selected folder
    inotifywait -m -e create,moved_to --format '%f' "$FOLDER_ORIGIN" |
    while read -r filename; do
        # Gets the file extension
        extension="${filename##*.}"
        # Checks if the extension is in the extension list
        for ext in "${EXTENSIONS_TO_WATCH[@]}"; do
        if [[ "$ext" = "$extension" ]]; then
            # Check if the file name starts with "optimized"
            if [[ "$filename" != optimized* ]]; then
                filename_output="optimized_${filename%.*}.mp4"
            # Displays a flat file of information
            touch "$FOLDER_ORIGIN/$MESSAGE_WAITING"
            # Convert the file to MP4 format using ffmpeg in /tmp/
            ffmpeg -i "$FOLDER_ORIGIN/$filename" -c:v libx264 -tune stillimage -c:a aac -b:a 192k -pix_fmt yuv420p -nostdin -shortest "/tmp/$filename_output"
            # When finished move the optimized file
            mv "/tmp/$filename_output" "$FOLDER_ORIGIN/$filename_output"
            # Remove a flat file of information
            rm "$FOLDER_ORIGIN/$MESSAGE_WAITING"
            fi
        fi
        done
    done
}

# CONTROLE ARGUMENTS
isArg=""

while [ $# -gt 0 ] ; do
    case "$1" in
    --help)
        usage
        ;;
    --folder)
        isArg="1"
    if [ $# -eq 2 ]; then
        start
    else
        usage "You need to specify the path of the folder to watch."
    fi
        ;;
    *)
    esac
    shift
done

if [ -z $isArg ] ; then
    usage "Not enough arguments"
fi

Now run:

bash-folders-video-optimizer --folder [folder to watch]

Persistence

Do you want execute the after script every boot your computer?

Open your cron:

crontab -e

And insert this line:

@reboot bash-folders-video-optimizer --folder [folder to watch] >/dev/null 2>&1 &

Conclusion

I hope this trick helps you to optimize your time. If you want to see more examples, I recommend you to visit the repository Bash folders: images optimizer, battery hooks, etc. I will be happy if you contribute with your own scripts.

See you in the next post!