Recently I received some RTF files via email. I wanted to read them on my phone, but I didn’t have any apps installed which understood RTF. I thought it would be nice to have a tool in Termux which would dump nicely formatted RTF to the terminal. At first I thought I might write something to do this myself, but then I discovered unrtf.

unrtf will read an RTF file and can output plaintext or html, among other formats. This sounded like exactly what I was looking for. However, it was not available in the Termux repositories. Never fear! I’ll build it from source I thought. However, I couldn’t install clang on in Termux because my phone didn’t have enough storage space.

This brought me to cross-compiling, which I haven’t done much (any?) of before. I started to look into cross compiling with clang, which might have worked, but then I remembered reading an article about how zig cc could be used for cross-compiling. I also learnt that zig has a built-in musl libc, and supports multiple target architectures out of the box.

It took me a bit of time to figure out the correct invocation to run the build, but it ended up quite simple:

tar -xf unrtf-0.21.10.tar.gz
cd unrtf-0.21.10
./configure CC="zig cc -target arm-linux-musleabi -D_GNU_SOURCE" --host=arm-linux-musleabi

After this, I had a 32 bit arm unrtf binary on my computer at src/unrtf. I created an archive containing this and the outputs/ directory and copied it to my phone. (The outputs directory is required, and must be specified when running unrtf if it is not installed to the standard location.) I then ran the executable as follows, which by default outputs HTML to stdout:

unrtf -P outputs file.rtf

Finally, I piped the output to the lynx CLI browser:

unrtf -P outputs file.rtf | lynx -stdin

This produced very readable output!