C++ popen() fails to capture output from bash pipeline commands on Ubuntu 22.04 while working on Debian 11 [closed]

I'm building a simple process monitoring tool that needs to execute and capture bash command outputs through C++. The weird part: same commands work perfectly in terminal but fail through C++.

Code:

#include <cstdio>#include <iostream>#include <memory>#include <string>#include <array>std::string exec_command(const char* cmd) {    std::array<char, 128> buffer;    std::string result;    std::unique_ptr<FILE, decltype(&pclose)> pipe(popen(cmd, "r"), pclose);    if (!pipe) {        throw std::runtime_error("popen() failed!");    }    while (fgets(buffer.data(), buffer.size(), pipe.get()) != nullptr) {        result += buffer.data();    }    return result;}int main() {    // Simple reproducible example    const char* test_cmd = "ps aux | grep bash";    std::cout << "Running: " << test_cmd << std::endl;    try {        std::string output = exec_command(test_cmd);        std::cout << "Output: " << output << std::endl;    } catch(const std::exception& e) {        std::cerr << "Error: " << e.what() << std::endl;    }    return 0;}

Environment (Reproducible on):

• OS: Ubuntu 22.04 LTS
• Compiler: GCC 11.3.0 (g++ --version output below)
• Shell: Bash 5.1.16

g++ (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0

Terminal vs Program Output:

Terminal output (works):

$ ps aux | grep bashroot      1234  0.0  0.1   9720  5236 pts/0    Ss   10:00   0:00 -bashuser      5678  0.0  0.1   9720  5236 pts/1    Ss+  10:01   0:00 bash

Program output (fails):

$ ./a.outRunning: ps aux | grep bashOutput: 

Debug Information:

strace output snippet:

$ strace ./a.out...pipe2([3, 4], O_CLOEXEC)               = 0clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f9b2c7fe9d0) = 12345...

What I've tried (in order):

1. Basic troubleshooting:
   • Running with sudo
   • Using system() instead of popen()
   • Different buffer sizes
2. Advanced debugging:
   • strace monitoring
   • valgrind memory checks
   • Different shell commands without pipes

Expected behavior:

Program should capture and display the same output as running the command directly in terminal.

Question:

What's causing this discrepancy between terminal and C++ execution, and how can I properly capture piped command output in Ubuntu 22.04?

Notes:

• No error messages or return codes
• Works fine on Debian 11 with same GCC version
• All files/processes have correct permissions
• Issue happens with any piped command, not just this example...