Content-type: text/html Man page of p2open

p2open

Section: String Pattern-Matching Library Functions (3GEN)
Updated: 29 Dec 1996
Index Return to Main Contents
 

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.  

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().  

EXAMPLES

Example 1: Example of file descriptors.

#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);
}

 

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPEATTRIBUTE VALUE
MT-LevelUnsafe

 

SEE ALSO

fclose(3C), popen(3C), setbuf(3C), attributes(5)  

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(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.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUES
EXAMPLES
ATTRIBUTES
SEE ALSO
NOTES

This document was created by man2html, using the manual pages.
Time: 02:39:53 GMT, October 02, 2010