[SOLVED] Is there similar commands to getprop/setprop in Linux or Mac?

cloudytechi147 · 10-25-2021, 09:13 AM

I'm wondering if there are similar commands to getprop/setprop that exist in Android.

I want to enable to do changes for certain properties for a compiled app without compiling it again.

I know that on Android I can do so with ADB shell setprop but I didn't find something similar in Linux/Mac.

There is a way to do something like that with environment variable on the best Linux distribution (maybe the same thing on Mac) but is there something else?

I'll give an example of what I want to do: Let's say that I have a program that uses a default number of threads for parallelization and I want to change the number of threads after compilation. I can do so by adding an environment variable, setting it in my session then running my app.

The following code demonstrates this:

Code:

#include <sstream>
#include <cstdlib>

template <class T>
bool getEnv(const char* envVariable, T& value) {
    auto envValue = getenv(envVariable);
    if (!envValue) {
        return false;
    }
    if constexpr (std::is_same_v<T, int>) {
        auto tempValue = strtol(envValue, nullptr, 10);
        if (tempValue < std::numeric_limits<int>::min() ||
             tempValue > std::numeric_limits<int>::max()) {
            return false;
        }
        value = tempValue;
    } else if constexpr  (std::is_same_v<T, double>) {
        auto tempValue = strtod(envValue, nullptr);
        if (tempValue < std::numeric_limits<double>::min() || 
             tempValue > std::numeric_limits<double>::max()) {
            return false;
        }
        value = static_cast<double>(tempValue);
    } else {
        // make sure this won't compile
        static_assert(!std::is_same_v<T, T>);
    }
    return true;
}

int main() {
    int number_of_threads;
    int status = getEnv("NUMBER_OF_THREADS", number_of_threads);
    if (!status) {
        std::cerr << "Failed to get NUMBER_OF_THREADS\n";
        return 1;
    }
    std::cout << "NUMBER_OF_THREADS=" << number_of_threads << "\n";

    return 0;
}

On the terminal:

Code:

idancw:~/envTest/cmake-build-debug> export NUMBER_OF_THREADS=4
idancw:~/envTest/cmake-build-debug> ./test 
NUMBER_OF_THREADS=4
idancw:~/envTest/cmake-build-debug> export NUMBER_OF_THREADS=10
idancw:~/envTest/cmake-build-debug> ./test                     
NUMBER_OF_THREADS=10

Is there another way to do so without using the env variable, similar to Android?

I gauss that I can use the env approach on Mac too, but there is something else?

Thanks

Keith Hedger · 10-27-2021, 08:37 AM

short answer:
no
slightly longer answer:
if the application has a prefs file you may be able to tweak it from there, but it would depend on the app.

Guttorm · 10-28-2021, 08:36 AM

Yes, environment variables are not the solution here. The program gets a copy of all of them when the program starts, and getenv will not get updated values.

What you can do, is to setup a signal handler function. It's usually used for error handling and cleanup, but SIGUSR1 and SIGUSR2 can be used for anything.

Code:

#include<stdio.h>
#include<signal.h>
#include<unistd.h>

void sig_handler(int signum){
  // Here we can e.g. read a config file, and update variables
  printf("\nInside handler function\n");
}

int main(){
  signal(SIGUSR1,sig_handler); // Register signal handler
  for(int i=1;;i++){    //Infinite loop
    printf("%d : Inside main function\n",i);
    sleep(1);  // Delay for 1 second
  }
  return 0;
}

You can then use commands like "killall -USR1 test" or kill -USR1 pid to tell the app it should read a config file or something.