is not "a process" but in fact the shell creates two such processes: one for "command1", one for "command2". You need to execute the procedure of using execvp() or fork() for both of them because both are processes in their own right. Only then you need a provision for the pipeline functionality.
A (shell-) pipeline is to connect STDOUT of the one process to the STDIN of the other. But this means there are already two process-environments with such file descriptors that can be connected. Here is a thread that might give you the picture: Trouble with pipes in chat client on linux.
I have a function that returns a bunch of exit codes, say func1, and in my code I'm trying to execute that function in an if statement. This is the closest I could get.
f1call=`func1 $arg1 $arg2`
if ]; then
...
fi
When I run the script the function never gets called. What's the right way... (7 Replies)
Hi ,
I m actually trying to implement pipes program,but after executing the execvp(),my program is getting hanged up :mad:
Actaully i m getting the desired output expected from execvp()...but once results are displayed on the output screen ,program is getting hanged up
values of... (3 Replies)
In a BASH library I'm creating, I have two functions that look like:
function check_process {
PIDFILE=$1
if ; then
PID=`cat $PIDFILE`
if && ; then
return 1
fi;
fi;
return 0
}
function fork_process {
CMD=$1
PIDFILE=$2
... (2 Replies)
I want to log into a remote server transfer over a new config and then backup the existing config, replace with the new config.
I am not sure if I can do this with BASH scripting.
I have set up password less login by adding my public key to authorized_keys file, it works.
I am a little... (1 Reply)
Hi Folks,
I have a small doubt, the binary commands under /bin and /sbin as well as other path binary files, if you peek deep into that, you can find the difference in the way of normal perl programming and some commands will be like binary files. how are the commands executing like the... (3 Replies)
Hi,
I want to run these two commands one after the other.
awk 'BEGIN {OFS="\t"} {print $2}'
sort -u
rather than typing awk 'BEGIN {OFS="\t"} {print $2}' file1 > file2, then sort -u file2 > file3. Is it possible to run both commands on file1 then get output file3?
Its kinda hard for... (5 Replies)
Hi, I do the following:
i) malloc some parameter structures
ii) fork
iii) in the child, I call execvp using these parameters
obviously, here I can never free() the structures as execvp should not return
iiii) I am currently doing waitpid in parent then freeing, but this does not seem to work... (1 Reply)
I have a script that writes another script with
cat >/usr/local/bin/myscript.sh <<EOF
#!/bin/sh
VAR=`run a command here`
EOF
Problem is, after this is run, I get:
$ cat /usr/local/bin/myscript.sh
#!/bin/sh
VAR=result of command
How do I stop that from happening with Macs... (2 Replies)
Ksh is my default shell, but I want use the bash shell since its convenient to me.
When I type a long command line in a terminal, it does not wrap to the next line when I reach the end of the line and it wraps onto the same line, overwriting my prompt and the rest of what I typed.
$... (5 Replies)
I have a script that checks if the script has been ran with sudo.
If the script is not ran as sudo, the current script is being executed with exec sudo bash.
You are asked for a password, you type in the password, success. Everything is perfect - the commands inside the script are ran as sudo.... (1 Reply)
Discussion started by: boqsc
1 Replies
LEARN ABOUT ULTRIX
pipe
pipe(2) System Calls Manual pipe(2)Name
pipe - create an interprocess channel
Syntax
include <limits.h> /*Definition of PIPE_MAX*/
pipe(fildes)
int fildes[2];
Arguments
fildes Passing an address as an array of two integers into the system call.
Description
The system call creates an I/O mechanism called a pipe. The file descriptors returned can be used in and operations. Their integer values
will be the two lowest available at the time of the function call. The O_NONBLOCK and FD_CLOEXEC flags will be clear on both file descrip-
tors.
When the pipe is written using the descriptor fildes[1], up to PIPE_MAX bytes of data are buffered before the writing process is suspended.
A read using the descriptor fildes[0] picks up the data.
It is assumed that after the pipe has been set up, two (or more) cooperating processes (created by subsequent calls) pass data through the
pipe with and calls.
The shell has a syntax to set up a linear array of processes connected by pipes.
For further information on how and calls behave with pipes, see the and reference pages.
A signal is generated if a write on a pipe with only one end is attempted.
Restrictions
Should more than 4096 bytes be necessary in any pipe among a loop of processes, deadlock may occur.
The underlying implementation of pipes is no longer socket based, but rather implemented through the file system. Any application that
needs socket functionality from pipes should use the system call.
Return Values
The function value zero is returned if the pipe was created; -1 if an error occurred.
Diagnostics
The call fails if:
[EMFILE] Too many descriptors are active.
[ENFILE] The system file table is full.
[EFAULT] The fildes buffer is in an invalid area of the process's address space.
Environment
Differs from the System V definition in that ENFILE is not a possible error condition.
See Alsosh(1), fork(2), read(2), socketpair(2), write(2)pipe(2)