I Wrote code that forks into two processes, a parent process, and a child process. The parent process will take the arguments to main() and send them one character at a time to the child process through a pipe (one call to write for each character). The child process will count the characters sent to it by the parent process and print out the number of characters it received from the parent.
The child should return normally (in other words, do not have the parent kill the child).
For some reason when my program executes, once in a while the command line prompt will come up before my program is done outputting. so basically the commandline gets a line of my output.. So I just press enter and everything is OK.
Hi
I have a C++ program that generates a lot of log information on the console, I need this output (printed using printf function) to go to a file since I will use crontab to schedule the job.
I know I can do this:
myprog > myfile
but I don't know how to enter this in crontab.
I use... (3 Replies)
Hello
I wander if im doing :
ls -l and its giving me lets say 3 results :
-rw-r--r-- 1 blah other 1789 May 19 2003 foo.c
-rw-r--r-- 1 blah other 1014 May 19 2003 foo.h
-rw-r--r-- 1 blah other 270 May 19 2003 foo1.c
now I would like to use the first... (1 Reply)
The output I got for this pgm is "4 4 4 4".
Can any one help me to understand how I got this output.
Also please suggest me some links to learn about argumnets evaluation in C.
# include <stdio.h>
void func(int a, int b, int c, int d)
{
printf("%d %d %d %d", a, b, c, d);
}
int... (3 Replies)
Hello All,
iam a new memeber today i joined this forum.
hope i will get help. the below program takes input strings and give reverse of input string.
&& mv /home/test1/programs/display /home/test1/programs/old
echo " Please enter the test "
read a
echo "$a" > file
wc -c file > file1
perl... (1 Reply)
Hi All,
I have created a sample perl program in one of the unix environment as below
#!/usr/bin/perl
print "Content-type: text/html\n\n";
print "<H1>Hello World</H1>";
When I execute it in unix, I get the below
Content-type: text/html
<H1>Hello World</H1>
However, when I... (1 Reply)
hi,
i have posted the same kind of the question in some other forum of the same site. but realized that it is supposed to be here so i am reposting it .this is the perl script written to check for particular pattern.
my file 1 would look like this
hwk:678:9878:asd:09: abc cfgb 12 nmjk ......... (3 Replies)
Discussion started by: anurupa777
3 Replies
LEARN ABOUT LINUX
pipe
PIPE(2) Linux Programmer's Manual PIPE(2)NAME
pipe, pipe2 - create pipe
SYNOPSIS
#include <unistd.h>
int pipe(int pipefd[2]);
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <unistd.h>
int pipe2(int pipefd[2], int flags);
DESCRIPTION
pipe() creates a pipe, a unidirectional data channel that can be used for interprocess communication. The array pipefd is used to return
two file descriptors referring to the ends of the pipe. pipefd[0] refers to the read end of the pipe. pipefd[1] refers to the write end
of the pipe. Data written to the write end of the pipe is buffered by the kernel until it is read from the read end of the pipe. For fur-
ther details, see pipe(7).
If flags is 0, then pipe2() is the same as pipe(). The following values can be bitwise ORed in flags to obtain different behavior:
O_NONBLOCK Set the O_NONBLOCK file status flag on the two new open file descriptions. Using this flag saves extra calls to fcntl(2) to
achieve the same result.
O_CLOEXEC Set the close-on-exec (FD_CLOEXEC) flag on the two new file descriptors. See the description of the same flag in open(2) for
reasons why this may be useful.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
ERRORS
EFAULT pipefd is not valid.
EINVAL (pipe2()) Invalid value in flags.
EMFILE Too many file descriptors are in use by the process.
ENFILE The system limit on the total number of open files has been reached.
VERSIONS
pipe2() was added to Linux in version 2.6.27; glibc support is available starting with version 2.9.
CONFORMING TO
pipe(): POSIX.1-2001.
pipe2() is Linux-specific.
EXAMPLE
The following program creates a pipe, and then fork(2)s to create a child process; the child inherits a duplicate set of file descriptors
that refer to the same pipe. After the fork(2), each process closes the descriptors that it doesn't need for the pipe (see pipe(7)). The
parent then writes the string contained in the program's command-line argument to the pipe, and the child reads this string a byte at a
time from the pipe and echoes it on standard output.
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
int
main(int argc, char *argv[])
{
int pipefd[2];
pid_t cpid;
char buf;
if (argc != 2) {
fprintf(stderr, "Usage: %s <string>
", argv[0]);
exit(EXIT_FAILURE);
}
if (pipe(pipefd) == -1) {
perror("pipe");
exit(EXIT_FAILURE);
}
cpid = fork();
if (cpid == -1) {
perror("fork");
exit(EXIT_FAILURE);
}
if (cpid == 0) { /* Child reads from pipe */
close(pipefd[1]); /* Close unused write end */
while (read(pipefd[0], &buf, 1) > 0)
write(STDOUT_FILENO, &buf, 1);
write(STDOUT_FILENO, "
", 1);
close(pipefd[0]);
_exit(EXIT_SUCCESS);
} else { /* Parent writes argv[1] to pipe */
close(pipefd[0]); /* Close unused read end */
write(pipefd[1], argv[1], strlen(argv[1]));
close(pipefd[1]); /* Reader will see EOF */
wait(NULL); /* Wait for child */
exit(EXIT_SUCCESS);
}
}
SEE ALSO fork(2), read(2), socketpair(2), write(2), popen(3), pipe(7)COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2010-09-10 PIPE(2)