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);
}

SEE ALSO

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

DIAGNOSTICS

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

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.