zsh 4.3.4% cat file
ACFCFACCACARCSHFARCVJVASTVAJFTVAJVGHBAJ
zsh 4.3.4% cat file1
A
C
F
R
zsh 4.3.4% <file1 while read;do printf "%s=%d\n" "$REPLY" "${#$(<file)//}";done
A=9
C=7
F=4
R=2
That was the previous post.
But , can anybody can explain me in detail about this line
zsh... (2 Replies)
this is the mksys b script....
can anyone explain .. what # and 1 in if condition
this is the first line of the script... it is not from middle of the script....
if
then
echo "Not enough parameters, need a client name for mksysb"
Usage="Usage: $0 <client name>"
... (2 Replies)
if
then
echo "Syntax: $0 <sid> <COLD/HOT> <DEST>"
exit
fi
if --------------what does this mean???
echo "Syntax: $0 <sid> <COLD/HOT> <DEST>"---pls explain this as well (2 Replies)
hi all i have an example i want one help me to understand cause i tried to test it but almost fail and i don't know how can i solve this problem " the main idea to read from two files and replace something from one to another " but i don't understand why it fail all time
$ cat main.txt... (4 Replies)
1. The problem statement, all variables and given/known data:
I have a retake assignment to complete for my computer networks and OS class. This isn't really my area, had I known last year I could have swapped it for a different module I would have done so. I'm determined to get through it... (6 Replies)
I'm trying to follow a script and I see it begins with this:
if ; then
if ; then
print "blah $0 blah blah "
exit
fi
fi
What does $# mean? I found out that $1 refers to the shell environment and the last argument that was entered or passed in the previous command. I couldn't find $#... (2 Replies)
Can someone do me a favour and explain the following for me:
((r=$RANDOM%$n+1))
I know what $RANDOM does but what is % sign and what does it do with %$n+1? (2 Replies)
Discussion started by: bashily
2 Replies
LEARN ABOUT MOJAVE
pipe2
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 <fcntl.h> /* Obtain O_* constant definitions */
#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_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 rea-
sons why this may be useful.
O_DIRECT (since Linux 3.4)
Create a pipe that performs I/O in "packet" mode. Each write(2) to the pipe is dealt with as a separate packet, and read(2)s from
the pipe will read one packet at a time. Note the following points:
* Writes of greater than PIPE_BUF bytes (see pipe(7)) will be split into multiple packets. The constant PIPE_BUF is defined in
<limits.h>.
* If a read(2) specifies a buffer size that is smaller than the next packet, then the requested number of bytes are read, and the
excess bytes in the packet are discarded. Specifying a buffer size of PIPE_BUF will be sufficient to read the largest possible
packets (see the previous point).
* Zero-length packets are not supported. (A read(2) that specifies a buffer size of zero is a no-op, and returns 0.)
Older kernels that do not support this flag will indicate this via an EINVAL error.
Since Linux 4.5, it is possible to change the O_DIRECT setting of a pipe file descriptor using fcntl(2).
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.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
On Linux (and other systems), pipe() does not modify pipefd on failure. A requirement standardizing this behavior was added in
POSIX.1-2016. The Linux-specific pipe2() system call likewise does not modify pipefd on failure.
ERRORS
EFAULT pipefd is not valid.
EINVAL (pipe2()) Invalid value in flags.
EMFILE The per-process limit on the number of open file descriptors has been reached.
ENFILE The system-wide limit on the total number of open files has been reached.
ENFILE The user hard limit on memory that can be allocated for pipes has been reached and the caller is not privileged; see pipe(7).
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, POSIX.1-2008.
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 file 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.
Program source
#include <sys/types.h>
#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), splice(2), tee(2), vmsplice(2), write(2), popen(3), pipe(7)COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the
latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Linux 2017-11-26 PIPE(2)