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p2open(3G)


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); }

References

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

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.

Notices

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.


© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004