I needed a simple popen2 implementation. This is similar to popen, but allows for bidirectional communication with the application being executed. Based on some other examples, I put this together. It makes for a good base.
Simple usage would be:
#include <sys/types.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #define READ 0 #define WRITE 1 pid_t popen2(const char *command, int *infp, int *outfp) { int p_stdin[2], p_stdout[2]; pid_t pid; if (pipe(p_stdin) != 0 || pipe(p_stdout) != 0) return -1; pid = fork(); if (pid < 0) return pid; else if (pid == 0) { close(p_stdin[WRITE]); dup2(p_stdin[READ], READ); close(p_stdout[READ]); dup2(p_stdout[WRITE], WRITE); execl("/bin/sh", "sh", "-c", command, NULL); perror("execl"); exit(1); } if (infp == NULL) close(p_stdin[WRITE]); else *infp = p_stdin[WRITE]; if (outfp == NULL) close(p_stdout[READ]); else *outfp = p_stdout[READ]; return pid; }
Simple usage would be:
int main(int argc, char **argv) { int infp, outfp; char buf[128]; if (popen2("sort", &infp, &outfp) <= 0) { printf("Unable to exec sort\n"); exit(1); } write(infp, "Z\n", 2); write(infp, "D\n", 2); write(infp, "A\n", 2); write(infp, "C\n", 2); close(infp); *buf = '\0'; read(outfp, buf, 128); printf("buf = '%s'\n", buf); return 0; }
When I tried using the code, I found I had to add several close statements. After
close(p_stdin[WRITE]);
dup2(p_stdin[READ], READ);
close(p_stdout[READ]);
dup2(p_stdout[WRITE], WRITE);
I added
close(p_stdout[READ]);
close(p_stdin[WRITE]);
since dup2 creates an extra copy of the file descriptors.
Just before
return pid;
I added
close(p_stdin[READ]);
close(p_stdout[WRITE]);
since the parent process has no business reading from the child's stdin our writing to its stdout.