Working with the Unix OS

Processes II
}
/* child */
signal (SIGTTIN, sigintHandler);
setpgrp(0, getpid()); /* place child in new process group */
printf("enter a string: ");
scanf ( "%s", str); /* try to read from control terminal */
printf("you entered %s\n", str);
} else
wait(&status); /* wait for child to terminate */
void sigintHandler()
{
printf("attempted inappropriate read from control terminal\n");
exit(1) ;
}
enter a string: attempted inappropriate read from control terminal
PIPES
Interprocess communication mechanism that allow two or more processes to send information to each other.
Used to connect standard output of one utility to standard input of another.
$ who | wc -1
Both the writer process and the reader process of a pipeline execute concurrently, a pipe automatically buffers the
output of the writer and suspends the writer if the pipe gets too full.
UNNAMED PIPES
pipe(fd) - unidirectional communication link
fd[0]----------------------------------------------------
write end | . |--->pipe--->| . | read end
fd[l]-----------------------------------
For bidirectional communication use two pipes
/* talk.c */
#include
#define READ 0
#define WRITE 1
char* phrase = "a line of text for talk";
main() {
int fd[2], nread;
char str[100];
}
pipe(fd); /* create unnamed pipe */
if(fork()== 0){ /* child writer */
close(fd[READ]); /* close unused end */
write(fd[WRITE], phrase, strlen(phrase)+1);
close(fd[WRITE]); /* close used end */
}
else
{/* parent reader */
close(fd[WRITE]); /* close unused end */
nread = read(fd[READ], str, 100);
printf("read %d bytes: %s\n", nread, str);
close(fd[READ]); /* close used end */
}
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