Popen

Popen is a term used in computing to describe facilities for spawning a new process and connecting to its input/output streams. The name is associated with two related APIs: the POSIX/C library function popen and Python's subprocess.Popen class.

In C, popen opens a process by executing a command through the system shell and returns a FILE* stream that can be read from (type "r") or written to (type "w"). It is simple and provides limited control over the child process. The corresponding pclose closes the stream and waits for the child to terminate. Because the command is interpreted by a shell, popen can be vulnerable to shell injection if used with untrusted input, and it typically offers less robust error handling and resource management than more explicit process creation APIs.

In Python, Popen is a class in the subprocess module that provides a highly controllable interface to spawn new processes and to connect to their standard streams. It accepts a list of arguments or a single string when shell is True, and it returns an object exposing attributes like pid and returncode and file-like objects for stdin, stdout, and stderr. Methods include communicate(), poll(), wait(), terminate(), and kill(). Optional parameters include cwd, env, stdout, stderr, stdin, shell, universal_newlines or text, encoding, bufsize, and close_fds.

Common considerations: avoid deadlocks by using the communicate() method or by employing non-blocking I/O strategies; be aware of platform differences when choosing options; consider security implications when invoking a shell. Popen is widely used for robust subprocess management, enabling flexible control over execution, I/O redirection, and lifecycle handling beyond simpler helpers like os.system or the basic popen interface.