p2open(3G)p2open(3G)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]);
DESCRIPTIONp2open 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);
}
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p2open(3G)p2open(3G)SEE ALSOfclose(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.
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