08-02-2008
/*
* here's how you can do it...
* using popen()
*
#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;
}
/*
* now in main... infp will be the stdin (in file descriptor)
* and outfp will be the stdout (out file descriptor)
* have fun
*/
int
main(int argc, char **argv)
{
int infp, outfp;
char buf[128];
if (popen2("your-program-B", &infp, &outfp) <= 0)
{
printf("Unable to exec your-program-B\n");
exit(1);
}
memset (buf, 0x0, sizeof(buf));
write(infp, "Z\n", 2);
write(infp, "D\n", 2);
write(infp, "A\n", 2);
write(infp, "C\n", 2);
close(infp);
read(outfp, buf, 128);
printf("buf = '%s'\n", buf);
return 0;
}
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LEARN ABOUT DEBIAN
filter_create_fd
filter_create_fd(3) util/filter.h filter_create_fd(3)
NAME
filter_create_fd - Create a sub process and return the requested pipes
SYNOPSIS
#include <util/filter.h>
NEOERR *filter_create_fd(const char *cmd, int *fdin, int *fdout, int *fderr,
pid_t *pid);
ARGUMENTS
cmd -> the sub command to execute. Will be executed with
/bin/sh -c
fdin -> pointer to return the stdin pipe, or NULL if you don't
want the stdin pipe
fdout -> pointer to return the stdout pipe, or NULL if you don't
want the stdout pipe
fderr -> pointer to return the stderr pipe, or NULL if you don't
want the stderr pipe
DESCRIPTION
filter_create_fd and filter_create_fp are what popen
been: a mechanism to create sub processes and have pipes to all their input/output. The concept was taken from mutt, though python has
something similar with popen3/popen4. You control which pipes the function returns by the fdin/fdout/fderr arguments. A NULL value means
"don't create a pipe", a pointer to an int will cause the pipes to be created and the value of the file descriptor stored in the int. You
will have to close(2) the file descriptors yourself.
RETURN VALUE
fdin -> the stdin file descriptor of the sub process
fdout -> the stdout file descriptor of the sub process
fderr -> the stderr file descriptor of the sub process
pid -> the pid of the sub process
SEE ALSO
filter_wait(3), filter_create_fp(3), filter_create_fd
ClearSilver 12 July 2007 filter_create_fd(3)