Working with the Unix OS

Processes II
/* connect.c - equivalent to command line pipe */
#include
#define READ 0
#define WRITE 1
main(int argc, char *argv[])
{
int fd[2], pipe(FILE *fd); /* create unnamed pipe */
}
if (fork()!= 0){ /* parent writer */
close(fd[READ]); /* close unused end */
dup2(fd[WRITE],1); /* duplicated used end to stdout */
close(fd[WRITE]); /* close original used end */
execlp(argv[1], argv[1], NULL); /* execute writer program */
fprintf(stderr, "connect"); /* should never execute */
}
else
{ /* child reader */
close(fd[WRITE]); /* close unused end */
dup2(fd[READ],0); /* duplicated used end to stdout */
close(fd[READ]); /* close original used end */
execlp(argv[2], argv[2], NULL); /* execute writer program */
fprintf(stderr, "connect"); /* should never execute */
}
connect who wc
NAMED PIPES - FIFO (first in first out)
Advantages:
- have a name that exists in file system
- may be used by unrelated processes
- exist until explicitly deleted
$ mknod mypipe p OR $ mkfifo mypipe
mknod(argv[l], S_IFIFO, 0);
chrnod(argv[l], 0660);
If a process tries to open a named pipe for read-only and no process writing, the reader will wait until a process
opens it for writing.
(If O_NDELAY is set then open succeeds immediately).
If a process tries to open a named pipe for write-only and no process reading, the writer will wait until a process
opens it for reading.
(If O_NDELAY is set then open fails immediately).
/* reader.c */
#include
#include
#include
#include
int mkfifo(char *name)
{
char str[100];
}
sprintf(str, "mkfifo %s", name);
return(system(str));
/* read NULL terminated line into str from fd */
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