NAME

p2open, p2close − open, close pipes to and from a command

SYNOPSIS

cc [ flag ... ] file ... −lgen [ library ... ]

#include <libgen.h>

int p2open(const char ∗cmd, FILE ∗fp[2]);

int p2close(FILE ∗fp[2]);

DESCRIPTION

p2open() 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. 

p2close() 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. 

EXAMPLES

#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 == 0 ) {
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);
}

RETURN VALUES

A common problem is having too few file descriptors.  p2close() returns −1 if the two file pointers are not from the same p2open(). 

SEE ALSO

fclose(3S), popen(3S), setbuf(3S)

NOTES

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(3S). 

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. 

SunOS 5.1/SPARC  —  Last change: 5 Jul 1990