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Thread: Linux Shell?

  1. Sep 25th, 2002, 09:40 PM #1
    rjlohan
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    Linux Shell?

    Anyone ever had a go at writing a Linux/Unix shell? Or know where I can find some good info or tutes?

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  2. Sep 26th, 2002, 06:43 AM #2
    parksie
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    No, but you can try and find the POSIX shell interface guidelines (the ones that bash is supposed to be following )
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  3. Sep 26th, 2002, 07:15 AM #3
    rjlohan
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    I know the POSIX guidelines I want to follow. More need implementation stuff. Especially about piping commands, and redirecting output/input...
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  4. Sep 26th, 2002, 07:16 AM #4
    parksie
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    popen(), perhaps?

    Or just look at the bash source.


    Probably the hardest part is the actually parsing interface, and this is where the readline library comes in...
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  6. Sep 26th, 2002, 07:32 AM #5
    rjlohan
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    I have the functions for opening and using a pipe, it's more the design. I'm pretty unfamiliar with Unix/Linux, so I only have a rough idea of how piping works.

    What's in the readline lib?

    I have a few things I have to do. The first is to make some inbuilt commands, like cd, etc. The second is to implement I/O redirect with >, < operators, and the last is piping.

    Gonna be quite a mission for a 2 week job...
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  7. Sep 26th, 2002, 07:34 AM #6
    rjlohan
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    P.S - I downloaded the bash source today. It's about...oh... 300 files...
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  8. Sep 26th, 2002, 07:37 AM #7
    parksie
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    Huge, isn't it.

    But that's because most shells are also programming languages


    The readline library does things like the history, command-line editing, stuff like that.
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  9. Sep 26th, 2002, 07:40 AM #8
    rjlohan
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    Sorry, exactly 820 files....
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  11. Sep 27th, 2002, 05:30 AM #9
    CornedBee
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    In addition to my PM, you might want to look at the glob function, it's quite useful.
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    CornedBee

    "Writing specifications is like writing a novel. Writing code is like writing poetry."
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  12. Sep 27th, 2002, 08:47 PM #10
    rjlohan
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    Will do. What's it do?
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  13. Sep 28th, 2002, 05:15 AM #11
    parksie
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    It performs "globbing", otherwise known as filename expansion. For example, if I glob the following:
    Code:
    mike@relativity ~] > ls *.txt {a,b,c}.dat
    it could possibly expand this to:
    Code:
    ls z.txt ache.txt lada.txt a.dat b.dat c.dat
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  14. Sep 28th, 2002, 06:57 AM #12
    CornedBee
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    Yes, I was right amidst writing a set of classes to do this when I stumbled upon this function.
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    CornedBee

    "Writing specifications is like writing a novel. Writing code is like writing poetry."
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  15. Sep 28th, 2002, 06:53 PM #13
    rjlohan
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    Ok, will check it out.
    Oh wait, that doesn't work here...
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