Simple Text Queue

Why and what it is

teaqueue is a command able to process sequentially items such as files from a list of filenames in a text files by calling a given command for each of them.

It can be used to:

transcode a batch of video files such as your preferred technical presentations to a format accepted by your mobile phone,
retrieve a bunch of URLs or other remote operation,
sequential operation on anything that can be encoded on a single line (json data, base64 data, etc).

It is really useful for operations taking a lot of time when you want to be able to stop processing items in the queue and resume it, optionally changing order of items or adding/removing items from it before.

Why tea ???

Because I love tea.

And this is a pun with the tee command since the teaqueue uses the same idea at his core.

Usage

Usage is linked directly to manipulation of simple text files. You use text files to make the queue, to add or remove items from it, to change priority of items. UNIX is the way.

I give some examples in this section. Take into account teaqueue takes queue.txt in the current directory by default as queue file modifying it when interrupted to remove processed items. By default, processed items goes to done.txt. This files serves to remove processed items from queue.txt when the queue is interrupted and serves as a log file for processed items.

Video batch transcoding

Firstly list filenames in the queue:

find -type f -iname '*.webm' > queue.txt

Then ask teaqueue to process each files with a transcoding command:

teaqueue transcode_my_file.sh

This is all if you just want to process each file and do not interrupt it. If you want to interrupt processing of the queue, modify it and resume it, first press Ctrl-C and modify queue.txt accordingly:

find ../another_dir -type '*.webm' >> queue.txt

Or reorder some items:

vim queue.txt

Then run again teaqueue:

teaqueue transcode_my_file.sh

transcode_my_file.sh is a simple script which calls ffmpeg or another program to convert your videos. The important point is the script should be able to be interruptible without interrupting the underlying job.

#!/bin/sh
[ "${FLOCKER}" != "$0" ] && exec env FLOCKER="$0" flock -e "$0" "$@"
ffmpeg -i "$1" -arg -arg &

The first ffmpeg command will go to background then, the second will wait until the first ffmpeg finishes. If the teaqueue command is interrupted, it can be run again without effectively interrupting the current ffmpeg job.

History

Normally, if you have a worker writing to standard output every file processed, you could write something like this:

find -iname '*.ext' > queue.txt
cat queue.txt | worker > done.txt
# here you can interrupt the service at any time (Ctrl-C/SIGTERM)
comm -23 queue.txt done.txt > remaining_queue.txt

But if this is something you want to do again and again, it might be convenient to write a little wrapper to do it for us. This is how teaqueue was born.