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 MINIX
fork
FORK(2) System Calls Manual FORK(2)NAME
fork - create a new process
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
pid_t fork(void)
DESCRIPTION
Fork causes creation of a new process. The new process (child process) is an exact copy of the calling process except for the following:
The child process has a unique process ID.
The child process has a different parent process ID (i.e., the process ID of the parent process).
The child process has its own copy of the parent's descriptors. These descriptors reference the same underlying objects, so that,
for instance, file pointers in file objects are shared between the child and the parent, so that an lseek(2) on a descriptor in the
child process can affect a subsequent read or write by the parent. This descriptor copying is also used by the shell to establish
standard input and output for newly created processes as well as to set up pipes.
The child starts with no pending signals and an inactive alarm timer.
RETURN VALUE
Upon successful completion, fork returns a value of 0 to the child process and returns the process ID of the child process to the parent
process. Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to
indicate the error.
ERRORS
Fork will fail and no child process will be created if one or more of the following are true:
[EAGAIN] The system-imposed limit on the total number of processes under execution would be exceeded. This limit is configuration-
dependent. (The kernel variable NR_PROCS in <minix/config.h> (Minix), or <minix/const.h> (Minix-vmd).)
[ENOMEM] There is insufficient (virtual) memory for the new process.
SEE ALSO execve(2), wait(2).
3rd Berkeley Distribution May 22, 1986 FORK(2)