Forking Processes Help!

[RickRoss]

Need a start on how to tackle this, thanks in advance!


Write a simple shell-like program that reads user commands and executes them using a combination of "fork", "exec", and "pipe".

history | head -10 | tail -5
Print the 6th through the 10th history commands. Your shell will have to set up a loop to create three processes and link them together using pipes so that the first child process runs "history" (and writes its output to a pipe), the second child process run "head" (with argument "-10"), reads from its standard input (which is the pipe into which the first child process writes) and writes to a pipe from which the third child process that runs "tail", reads. "tail" writes its output to the standard output.


The program has to take into account Pipes | and input and output redirection <, >. There are presumably no wrong inputs. i.e. the commands are all linux commands. Also the pipes are not finite meaning that input can be any number of pipes or redirections

Any advice would be greatly appreciated!

[laasunde]

My advice is that you should make an effort yourself and post here if you have more specific question(s).

[g_gili]

Here are some reference examples :
FORK
Exec
PIPES


Good luck,
Gili

[RickRoss]

Okay

I need to read in an input line something like

ls -l | sort - n -r | head

I have a struct to do this, something like:

struct getCommand
{
string command;
vector < string > args;
int numPipes;
};

So in my main() I will need to read the first string ("ls" in this example) and store it as a command string, then i need to store the arguments of that command (everything leading up to a '|' character) into a vector so I can call execvp on them later in the program. And then of course I need to parse to count the number of Pipes in the input.

The catch is, I need to loop this until '\n' reading any number of commands, args and pipes and I'm not sure on the syntax to do this exactly.

Thanks for help in advance

[Stiff Dikc in u FACE]

Dear Mr. Ross,

I feel that you will find the following steps helpful:

1) in parent, pipe ur 2 element p1 and p2, close the write end of the p1[1]
2) fork
3) in child, dup2 ur p1 for reading and dup2 ur p2 for writing
4) execute ur command
5) close both ends of ur p1 and ur p2 in child then kill your child!

then..
6) in parent process, close ur p2 write
7) stick it up u face and shake it shake it!! u make me sick! learn how to code before you flex nuts. read a book or something.

Cordially yours,

Dr. Stff in u FACE

P.S. I am gay

[aewarnick]

It's good to see more and more people programming for Linux and other operating systems besides M$ Windows.