P2OPEN(3GEN) String Pattern-Matching Library Functions P2OPEN(3GEN)


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


The p2open()gfunction 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.


The p2close() function 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. The p2close()
function 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 TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|MT-Level | Unsafe |
+---------------+-----------------+

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.


December 29, 1996 P2OPEN(3GEN)