Programming

Thank you so much. Can I say that "nano" or "vi" is a process and a command like "ls | grep .c" is a job?

And while implementing pipes, when I issue a command such as "ls | grep .c" in my interpreter, after parsing it, what should I be doing? I read about file descriptors and am assuming the following has to be done:

1. Parse the command line
2. argv[0] contains ls, so fork a process and execute it but redirect the output to a file (I don't know how this can be done internally in the C Code. I know I need to use the execv command to execute but how will I redirect?)
3. In the next parse, I scan the "|" character and so I know that the user wants to pipe the output and at this stage I would fork another process with the argv[2] string i.e. "grep .c" (but this will be stored in argv[2] and argv[3]. How will I know that the second one has command line arguments too and how should I handle them?) and then direct the output of this to the stdout.

Please let me know if the above steps are ok...

First of all, all the commands you specified are processes. nano will be one process, vi will be another. "ls | grep xyz" will create two processes, one for the ls and the second for the grep. A job is what the interpreter (the shell) handles internally. A job may consist of one or more processes. It is basically a one or more processes that the shell treats as a single unit when, say, handling signals.

As for your second question, shouldn't you ask your college instructor for help with your homework? But overall, you are on the right track. Choose your seperators well. White space (spaces and tabs) can come in the course of a single command. But a | or a newline (\n) are definitely command seperators. Treat them as such.

Not exactly a homework(I'm a research student doing this in my free time so that I can get a grip on Unix) but doing it out of curiosity... And well, I am not asking for a solution here... I am writing down my thoughts and asking if its right or wrong... Anyways if you feel I shouldn't get any help, I respect your decision but please consider that I'm a beginner...

By the way, thanks for the explanation of a job and a process. That makes a lot of things clear...

I'm not saying that you shouldn't get any help at all, in fact, you are actually making an effort to do this yourself, while most people just ask for code.

Just that it is against forum rules to post homework questions.

I'm looking forward to using "lsh" when Legend986 is done, it looks good so far.

Well I understand... But thats my point, I'm not in search of a solution or the code... I'm not a Computer Science student and I've made this point clear almost a few weeks back in the same forum and need some help in learning all this because I'm lost at a few places... Well, even then what you say is right... Even though this is not my homework, I now understood your reason - these "homeworks" are given in many universities... lol

I don't quite remember using the term lsh anywhere... Can you please tell me what it is? Or by any chance did you give a name to my shell?

Legend986 shell.