To emulate subprocess.check_call("Program1 | Program2", shell=True)
Python call, you could use system(3)
in C:
/** $ gcc simple-pipe-system.c && ./a.out */
#include <stdlib.h>
int main(void) {
return system("Program1 | Program2");
}
Here's how to emulate Program1 | Program2
pipeline using low level pipe(2)/fork(2)/execlp(2) in C for comparison:
/** $ gcc simple-pipe.c && ./a.out */
#include <sys/types.h> /* pid_t */
#include <unistd.h>
int main(void) {
int fd[2]; /* pipe ends */
pid_t pid = -1;
if (pipe(fd) == -1)
Report_error_and_exit("pipe");
if ((pid = fork()) == -1)
Report_error_and_exit("fork");
else if (pid == 0) {
/* child: run Program1, redirecting stdout to the pipe */
is_child = 1;
Close(fd[0]); /* close unused read end of the pipe */
/* redirect stdout */
Redirect(fd[1], STDOUT_FILENO);
/* run Program1 with redirected stdout */
execlp("Program1", "Program1", NULL);
Report_error_and_exit("execlp");
}
/* parent: run Program2, redirecting stdin to the pipe */
Close(fd[1]); /* close unused write end of the pipe */
/* redirect stdin */
Redirect(fd[0], STDIN_FILENO);
/* run Program2 with redirected stdin */
execlp("Program2", "Program2", NULL);
Report_error_and_exit("execlp");
}
where Report_error_and_exit, Close, Redirect could be defined as:
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#define Close(FD) do { \
const int Close_fd = (FD); \
if (close(Close_fd) == -1) \
fprintf(stderr, "%s:%d: close(" #FD ") %d: %s\n", \
__FILE__, __LINE__, Close_fd, strerror(errno)); \
}while(0)
#define Report_error_and_exit(msg) do { \
fprintf(stderr, "%s:%d: %s: %s\n", __FILE__, __LINE__, \
(msg), strerror(errno)); \
(is_child ? _exit : exit)(EXIT_FAILURE); \
} while(0)
static int is_child = 0;
#define Redirect(FROM, TO) do { \
const int from = (FROM); \
const int to = (TO); \
if (from != to) { \
if (dup2(from, to) == -1) \
Report_error_and_exit("dup2"); \
else \
Close(from); \
} \
} while(0)