A shim library that both works to allow shell scripts to execute correctly on iOS, and provides a framework for true rootless support.
A build of libiosexec is provided on Procursus, which you can install if your device is already setup with the build system.
Alternatively, you can compile libiosexec on your device using Git and Make. Run the commands below to build the project
make install DESTDIR="/install/path"
There are other variables you can specify when building; checkout the Makefile.
There's not that much to say here; simply define the symbols in your project/script
/* Wrapper functions to make iOS shells scripts function correctly */
#include <libiosexec.h>
Note that this implementation follows FreeBSD/Linux behavior of not splitting the argument passed to the shebang, unlike macOS which does.