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