Write programs for Android without writing apps

This program takes only 267 bytes, the code is easy to inspect and understand.

Compare it with easydice; the APK is 9MiB in size, a gigantic monster in comparison!

It is possible to create smaller programs, like diedroid. It is "only" 0.9Mib; the code required for making such a program is a lot compared to the bash script.

Depending on your use case, this bash script might not be enough. For example, the input of the user is not validated. Also using % is problematic, as the generated numbers are not uniformly distributed. Some values might have a higher chance of appearing than others. Both apps do not have this issue, the input is validated and they use java.lang.Random.nextInt, which creates uniformly distributed numbers in a given interval.

The point still stands, writing a uniformly distributed dice in bash might be hard, but it is possible to use python, awk, C++ or any other programming language you like, and replace $RANDOM % $max_value + 1 with program $max_value, or even implement the queries in your new program and replace the script entirely.

My current solution is to use speedtest-cli, as it is the same one used in many GNU/Linux distributions.

I have a wrapper for the Termux widget, as I tested the connection periodically for a given period:

Note that currently speedtest-cli requires 64K on disk. If the program wasn’t that lightweight, I would just store a bookmark to a webpage instead of installing a separate App, as an internet connection is required.

Instead of using adb, if possible, I prefer to use ssh for connecting to my Android device from my PC.

It is possible to optimize JPEG images to use less space without losing any quality. This is particularly useful when the disk is nearly full, or you want to share some images.

This script is not particularly efficient, because it tries to optimize serially every time all images For my use cases, it’s fast enough to get its job done.

It could be possible to store somewhere the information if a given image has already been optimized, and it is also possible to parallelize the optimization processes.

This shows how valuable it is to reuse existing programs; it makes it possible to reuse existing solutions without reinventing the wheel every time.

A slightly more complex interaction between my scripts is parsing a specific subreddit for a given pattern (and acting accordingly). Reddit offers an API ^🗄️ that serves JSON instead of HTML which, thanks to jq, is much easier to parse and transform.

The output is some pretty printed JSON, it might not be as user-friendly as a graphical application can be, but all I need to do is to copy some parts of the output, which is a two-click operation.

Termux offers also an API for reading SMS, which makes it possible to dump them and create a handy backup. With git/rsync/ssh and other programs it is easy to save all files automatically on another device, like a PC at home, when both are in the same network, without relying on external services. The best of it is that the tools I am currently using for backing up my computer are the same ones I’m using for Android.

Of course, I’m not counting the python and bash as dependencies when considering the complexity or size of a program, why should I?

I need to install those once and can use them multiple times for different tasks.

Android apps generally do not share libraries or other resources, which means they need more space both on the disk and in memory.

Also note that those programs can be executed and tested locally, on my PC, without any modifications or overhead. This has nothing to do with the fact that all examples are scripts, a C program can be compiled directly in Termux (it provides GCC) and on any Desktop system without modifications, as long as it does not use anything system-specific.

Most programs consist of 2 files; the program itself, saved in ~/bin or in some system directory, and a "launcher" in ~/.shortcuts.

The files that are not in ~/.shortcuts are responsible for doing the hard work, and generally do not interact with the user. This makes it simpler to reuse them in another context.

The scripts in ~/.shortcuts use whitespaces for separating words, as the script names appear in the Termux widget, and are thus more readable. They are also responsible for interacting with the user (querying values) and most important, thanks to printf 'Enter to close'; read -r ignore;, they avoid that the process finishes and the terminal window closes immediately.

Since Android 12 there are further limitations that seem to break Termux.

There are workarounds, but it makes Termux harder to use and seems to make the future of Termux uncertain.

Termux makes it easy to install and update programs, such as writing new ones, just like any GNU/Linux distribution or BSD system.

This breaks the security model of Android.

In Android, applications are isolated and can access only a subset of functionalities unless the end-user gives them the necessary permissions.

On Termux, all programs have the same permissions, unless special care is taken by the end user.

In one of the examples, I’m using jq. How do I know that jq, or for what is worth even simpler programs like cat or cd, do not have a "backdoor" and access my contacts and send them together with other personal information online?

I do not know, just like I do not know on a regular computer.

With an Android application, an end-user can be relatively sure that such things are not possible if a program does not have the necessary permissions. Of course, programs might exploit a vulnerability of the system, but that is another story.

Does it mean that one should not use Termux?

Just like every other application, one needs to trust the author(s) about what a program is doing.

In the case of Termux, there are a lot of functionalities packed together. The authors of Termux did not write all those programs from scratch, they rely on other existing programs that have been compiled for Termux.

Supposing that Termux itself is not malicious, the security model is the same as on a normal GNU/Linux distribution. As far as I know, repositories of GNU/Linux distributions, BSD systems, and Termux, never contained malware.

Nevertheless, it is a possibility, just like it is for every distribution system.

Other distribution systems like pypi, npm, the Google Play Store and App Store had malware at least once.

Maybe there is not enough interest (not big enough user base?), or maybe the fact that programs are compiled/packaged by the maintainers of the repository puts the bar on a much higher level.