90 lines
2.5 KiB
Text
90 lines
2.5 KiB
Text
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Sagi Dayan 2014
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-----------------------------
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OS course Ex1 - Home - cshell
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-----------------------------
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this project is a basic Terminal emulator written in C for OS course in JCE.
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This Terminal will be able to run almost all programs in the PATH /bin/<bin name>
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and will create a new process of that <bin name>.
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the Prompt format:
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<exit code> <userName>@<hostName>$
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the exit code is the Return code from the last child process.
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if 0 -> child ended successfully.
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for more details see Q&A
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sagi dayan (c) 2014.
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------------
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Build & Run & Exit
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------------
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To build cshell run in terminal: make
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and run with the command: cshell
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to quit run from cshell: exit
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to clean the directory run: make clean
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-------------------------
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Design Decisions & Issues
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-------------------------
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the main idea is to be able to run & create processes via commands.
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you can enter almost any basic command (and some more) that the binarys are in
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PATH /bin/ .
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Main issues:
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* you cannot navigate to different directories.
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* you cannot pipe command and arguments.
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* every word will be treated as an argumant!
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therefore you cannot write something like:
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$ ls -a > "my text.txt"
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cshell will see the arguments as:
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# ls
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# -a
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# >
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# "my
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# text.text"
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and that will throw you an error.
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-------
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Q&A
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-------
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Q: can i redirect output to a file?
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A: yes you can. use the "redirect" char '>' and then the file name.
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like so:
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$ man ls > myFile.txt
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Note: the content of the file Will be deleted, in othe words, it acts
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exactly like '>' in the UNIX Shell. not '>>'.
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Note2: the file name must be in one word. as you can see in Issues,
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cshell dose not support an argument that is seperated with space or tab.
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Q: what is that wired number before the prompt?
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A: that wierd number is atually the return code of the last process that you ran.
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the Unix defult return code of a succssesful end of process will be 0. otherwise,
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in case fo an error or an exception, the code can be any number (code) that the
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developer of that specific software maked down to exit at.
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Q: why 255?
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A: as i noticed, the defaul code of "exit(1)" is actually 256, but
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in the exersize wanted to return 255 in case of an "unknown command" or default
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exit(1).
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Q: why cant i exit cshell with ctrl-c (^C)?
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A: because that was also another task in this Ex.
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only running childes will be killed, while the main process (cshell)
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will stay running and kicking.
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Q: So how to exit?
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A: run 'exit'.
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Q: Can i redirect stderr output to file?
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A: No. the task was to implament only regular output.
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