popen_pclose实现

/*
 * popen.c Written by W. Richard Stevens
 */


#include
#include
#include
#include "ourhdr.h"


static pid_t *childpid = NULL;
/* ptr to array allocated at run-time */
static int maxfd; /* from our open_max(), {Prog openmax} */


#define SHELL "/bin/sh"


FILE *
popen(const char *cmdstring, const char *type)
{
int i, pfd[2];
pid_t pid;
FILE *fp;


/* only allow "r" or "w" */
if ((type[0] != 'r' && type[0] != 'w') || type[1] != 0) {
errno = EINVAL; /* required by POSIX.2 */
return(NULL);
}


if (childpid == NULL) { /* first time through */
/* allocate zeroed out array for child pids */
maxfd = open_max();
if ( (childpid = calloc(maxfd, sizeof(pid_t))) == NULL)
return(NULL);
}


if (pipe(pfd) < 0)
return(NULL); /* errno set by pipe() */


if ( (pid = fork()) < 0)
return(NULL); /* errno set by fork() */
else if (pid == 0) { /* child */
if (*type == 'r') {
close(pfd[0]);
if (pfd[1] != STDOUT_FILENO) {
dup2(pfd[1], STDOUT_FILENO);
close(pfd[1]);
}
} else {
close(pfd[1]);
if (pfd[0] != STDIN_FILENO) {
dup2(pfd[0], STDIN_FILENO);
close(pfd[0]);
}
}
/* close all descriptors in childpid[] */
for (i = 0; i < maxfd; i++)
if (childpid[ i ] > 0)
close(i);


execl(SHELL, "sh", "-c", cmdstring, (char *) 0);
_exit(127);
}
/* parent */
if (*type == 'r') {
close(pfd[1]);
if ( (fp = fdopen(pfd[0], type)) == NULL)
return(NULL);
} else {
close(pfd[0]);
if ( (fp = fdopen(pfd[1], type)) == NULL)
return(NULL);
}
childpid[fileno(fp)] = pid; /* remember child pid for this fd */
return(fp);
}


int
pclose(FILE *fp)
{


int fd, stat;
pid_t pid;


if (childpid == NULL)
return(-1); /* popen() has never been called */


fd = fileno(fp);
if ( (pid = childpid[fd]) == 0)
return(-1); /* fp wasn't opened by popen() */


childpid[fd] = 0;
if (fclose(fp) == EOF)
return(-1);


while (waitpid(pid, &stat, 0) < 0)
if (errno != EINTR)
return(-1); /* error other than EINTR from waitpid() */


return(stat); /* return child's termination status */
}