NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | ATTRIBUTES | SEE ALSO | NOTES
cc [ flag ... ] file ... -lgen [ library ... ] #include <libgen.h>int p2open(const char *cmd, FILE *fp[2]);
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.
A common problem is having too few file descriptors. p2close() 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:
ATTRIBUTE TYPE | ATTRIBUTE VALUE |
---|---|
MT-Level | Unsafe |
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.
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | ATTRIBUTES | SEE ALSO | NOTES