I have my inputfile in the following format :
From:sdhfhg
dsfhsdjfjdsfh
dsfjdjshjsd
djfhsdjfjsdhjds
Error Description
<aa.aa.aa.aa.aa.aa>
From:ksljfsdhfjh
djfdsjkf
sdjwoquk
dsfsdfj
Error Description
<dd.dd.dd.dd.dd>
I want to read the lines from tag 'From:' thrul <aa.aa.aa.aa.aa.aa>... (1 Reply)
Hello experts,
I am using fork() in my code but I am confused which output comes first child or parent?
I did the following code .My book shows parent first but my linux shows child first.Can anyone tell me why?
#include <stdio.h>
int main(){
int pid;
printf("I am original process with pid... (5 Replies)
Assume we have an application built on *nix that uses fork()...then the processes procedure is going to act as follow:
X is considered a parent process (first click on application)
Y is considered a child process of X (second click on application)
Z is considered a child process of Y (third... (6 Replies)
hi,
i start using awk and have a very basic problem. here's my code:
#! /usr/bin/awk -f
# 2010, scz
#
{
$1 == "test" { print $2 }
}
this works on the command line but not as "program" - what is the difference between awk programs on the command line and executing awk... (3 Replies)
I writing a program that forks three times but only on the parent process. The three children processes then produces output in order. 1, 2, 3. I am confused on how to do this. I have tried multiple if and else if statements but the output does not come out right. How should I go about doing this? (1 Reply)
Hello everybody.I want to make clear that i am not going to ask from anybody to build my asignement but i have a big problem. I can't seem to find anywhere ONE good example on C about what i am trying to do:wall:.I think it is simple. All i ask is one example, even a link is fine.
So, i want to... (1 Reply)
i'm experimenting fork function and i found this code
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <wait.h>
#include <fcntl.h>
#include <unistd.h>
int main(void)
{
int fd;
pid_t p;
p = fork();
fork();
if (p>0) { fork();}
fork();
fork();... (6 Replies)
Hi All,
I have a program for class that needs to do the following:
1. Print the directory entries from the current directory using ncurses
2. Provide a prompt next to each directory entry and allow the user to enter commands that may or may not be about the file
3. Execute those commands in... (1 Reply)
Hello... And thanks in advance for any help anyone can offer me on my question! I've been doing a lot of reading to try and find my answer... But I haven't had any luck
What I'm trying to understand is where a child process inherits global environment variables from? I understand the exec()... (2 Replies)
Discussion started by: bodisha
2 Replies
LEARN ABOUT NETBSD
popen
POPEN(3) BSD Library Functions Manual POPEN(3)NAME
popen, pclose -- process I/O
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
FILE *
popen(const char *command, const char *type);
int
pclose(FILE *stream);
DESCRIPTION
The popen() function ``opens'' a process by creating an IPC connection, forking, and invoking the shell. Historically, popen was implemented
with a unidirectional pipe; hence many implementations of popen only allow the type argument to specify reading or writing, not both. Since
popen is now implemented using sockets, the type may request a bidirectional data flow. The type argument is a pointer to a null-terminated
string which must be 'r' for reading, 'w' for writing, or 'r+' for reading and writing. In addition if the character 'e' is present in the
type string, the file descriptor used internally is set to be closed on exec(3).
The command argument is a pointer to a null-terminated string containing a shell command line. This command is passed to /bin/sh using the
-c flag; interpretation, if any, is performed by the shell.
The return value from popen() is a normal standard I/O stream in all respects save that it must be closed with pclose() rather than fclose().
Writing to such a stream writes to the standard input of the command; the command's standard output is the same as that of the process that
called popen(), unless this is altered by the command itself. Conversely, reading from a ``popened'' stream reads the command's standard
output, and the command's standard input is the same as that of the process that called popen().
Note that output popen() streams are fully buffered by default.
The pclose() function waits for the associated process to terminate and returns the exit status of the command as returned by wait4().
RETURN VALUES
The popen() function returns NULL if the fork(2), pipe(2), or socketpair(2) calls fail, or if it cannot allocate memory.
The pclose() function returns -1 if stream is not associated with a ``popened'' command, if stream has already been ``pclosed'', or if
wait4(2) returns an error.
ERRORS
The popen() function does not reliably set errno.
SEE ALSO sh(1), fork(2), pipe(2), socketpair(2), wait4(2), fclose(3), fflush(3), fopen(3), shquote(3), stdio(3), system(3)STANDARDS
The popen() and pclose() functions conform to IEEE Std 1003.2-1992 (``POSIX.2'').
HISTORY
A popen() and a pclose() function appeared in Version 7 AT&T UNIX.
BUGS
Since the standard input of a command opened for reading shares its seek offset with the process that called popen(), if the original process
has done a buffered read, the command's input position may not be as expected. Similarly, the output from a command opened for writing may
become intermingled with that of the original process. The latter can be avoided by calling fflush(3) before popen().
Failure to execute the shell is indistinguishable from the shell's failure to execute command, or an immediate exit of the command. The only
hint is an exit status of 127.
The popen() argument always calls sh(1), never calls csh(1).
BSD June 24, 2011 BSD