p2open, p2close - open, close pipes to and from a command
cc [ flag ... ] file ... –lgen [ library ... ] #include <libgen.h> int p2open(const char *cmd, FILE *fp[2]);
int p2close(FILE *fp[2]);
The p2open()gfunction forks and execs a shell running the command line pointed to by cmd. On return, fp[0] points to a FILE pointer to write the command's standard input and fp[1] points to a FILE pointer to read from the command's standard output. In this way the program has control over the input and output of the command.
The function returns 0 if successful; otherwise, it returns −1.
The p2close() function is used to close the file pointers that p2open() opened. It waits for the process to terminate and returns the process status. It returns 0 if successful; otherwise, it returns −1.
A common problem is having too few file descriptors. The p2close() function returns −1 if the two file pointers are not from the same p2open().
#include <stdio.h>
#include <libgen.h>
main(argc,argv)
int argc;
char **argv;
{
FILE *fp[2];
pid_t pid;
char buf[16];
pid=p2open("/usr/bin/cat", fp);
if ( pid == −1 ) {
fprintf(stderr, "p2open failed\n");
exit(1);
}
write(fileno(fp[0]),"This is a test\n", 16);
if(read(fileno(fp[1]), buf, 16) <=0)
fprintf(stderr, "p2open failed\n");
else
write(1, buf, 16);
(void)p2close(fp);
}
See attributes(5) for descriptions of the following attributes:
|
fclose(3C), popen(3C), setbuf(3C), attributes(5)
Buffered writes on fp[0] can make it appear that the command is not listening. Judiciously placed fflush() calls or unbuffering fp[0] can be a big help; see fclose(3C).
Many commands use buffered output when connected to a pipe. That, too, can make it appear as if things are not working.
Usage is not the same as for popen(), although it is closely related.