Another toy shell that serves no true purpose beyond being an engineer's µarch baby.
Learn more about my journey in developing the initial release of this shell on my website.
Builtins are predefined commands built into the shell.
If the first argument of a COMMAND (otherwise known as the WORD) is equal to
any of the builtin functions, then said builtin functions will be called instead
of being executed. This is true regardless if you have a valid form of the program
on your PATH.
help - prints a list of all builtins
dShell $ > help
----- dShell -----
Builtin commands:
~ cd
~ help
~ exit
cd - change the working directory
dShell $ > cd help
dShell $/help >
exit - terminate the shell
dShell $ > exit
Process finished with exit code 0
Logical operators provide a way for simple commands to be followed by other simple commands. Logical operators can not be followed or superseded by other logical operators.
AND [&&] - following command will only execute if the exit status is EXIT_SUCESS
dShell $ > ls
Testing
dShell $ > mkdir Testing && cd Testing
mkdir: cannot create directory ‘TestDirectory’: File exists
dShell $ > mkdir Testing2 && cd Testing2
dShell $/Testing2 >
OR [||] - following command will only execute if the exit status is NOT EXIT_SUCESS
dShell $ > ls
Testing
dShell $ > mkdir Testing && cd Testing
mkdir: cannot create directory ‘TestDirectory’: File exists
dShell $/Testing >
NOT [!] - flips the exit status of the following command
dShell $ > ls
Testing
dShell $ > ! mkdir Testing && cd Testing
mkdir: cannot create directory ‘TestDirectory’: File exists
dShell $/Testing >
ENDCOMMAND [;] - separates commands from one another
dShell $ > ls pwd
ls: cannot access 'pwd': No such file or directory
dShell $ > ls;pwd
Testing
/home/daymon/dShell/cmake-build-debug
Pipes (labeled PIPE or |) push the STDOUT of one command to the STDIN of another.
dShell $ > tail test.txt | grep "Hello"
Hello World!
Pipes must be precceded and followed by a COMMAND or SUBSHELL.
Preceeding or following PIPE with anything else is undefined.
Pipes are good for a single COMMAND.
To continue the PIPE, follow the COMMAND with another PIPE
Redirection allows you to write the STDOUT of a COMMAND to a specified file.
dShell $ > tail test.txt >> test2.txt
dShell $ > tail test2.txt
Hello World!
Redirection comes in two forms: REDIRECT_TO [>] and REDIRECT_TO_OVERWRITE [>>]. Both are
identical in nature, except that one appends the input to the file, wheres the other
overwrites the file to contain the input.
Redirection does not make any straight assumptions about your input. If you provide a complex command to a redirection, the redirection will evaluate the complex command and utilize the first string streamed to STDOUT as the input (or output). What this means is that you can do things like this:
dShell $ > tail test.txt > (cd ./testdirectory && ls && grep "test3")
You are not limited to programs either, you can provide either the input or output as straight string literals.
dShell $ > "Hello world!" > test3.txt && "Goodbye world!" >> test3.txt
dShell $ > tail test3.txt
Hello world!
Goodbye world!
Subshells allow you to branch execution into a seperate process.
dShell $ > (cd Test && pwd)
/home/daymon/dShell/cmake-build-debug/Test
dShell $ > pwd
/home/daymon/dShell/cmake-build-debug
Initilized with a SUBSHELL_START [(] and ended with a SUBSHELL_END [)],
these two symbols create a SUBSHELL.
Subshells also support pipes!
dShell $ > (cd Test && tail test.txt) | grep "Hello"
Hello World!
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Fix open issues
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Generate unit tests for everything
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Implement addition builtins
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Add support for pre-evaluated arguments