Run a shell designed to mimic sh. Execute commands and interact with the kernel.

simplesh [script files]

• Run commands in $PATH
• Environment and local variables
• $? return values, $$ pid
• $# number of args and $0-9 (not a perfect sh mimic currently though)
• Logical operators &&/|| with multi-line continuation
• ; command separator
• ~ expansion to current user's home directory
• unclosed multi-line quote continuation
• \ escaping
• Run script files, as well as commands from standard input

Built-ins:

• help
• exit [status]
• setenv
• unsetenv
• env (listing environment functionality only)
• cd
• alias
• unalias
• history

To use this shell, we want to compile it and move it into a $PATH folder like /usr/local/bin. To compile the program, clone the project, navigate to the directory, and then type:

gcc -o simplesh *.c

The copy the output file to /usr/local/bin (you may need to add "sudo" to the front of this line):

cp simplesh /usr/local/bin

After this you should be able to run the shell by typing "simplesh".

To start up the shell and run a simple command (in this case pwd), then exit:

Username@your-regular-prompt:~$ simplesh
simplesh:/home/username$ pwd
/home/username/
simplesh:/home/username$ exit
Username@your-regular-prompt:~$

pwd lists the current working directory, which is displayed in the simplesh terminal prompt. We can also run script files. If we have a script with the following:

#!/usr/bin/env simplesh
echo Hello from simple shell!

Then execute the script we will see "Hello from simple shell!" in our terminal. We can also use command line arguments for variables. Currently, $0 is always "simplesh", $1 is the script name, and $2 and beyond are the arguments. So if we want the first argument, we would put in $2 like so:

#!/usr/bin/env simplesh
echo Hello $2

Then if we want to pass in an argument we can do it like so:

Username@your-regular-prompt:~$ ./helloscript "simple shell!"
Hello simple shell!

There is a repository for the test suite at https://github.com/sidneyriffic/shelltest.git. Follow the instructions there, and you'll want the shell target to be /bin/sh (the default location for sh).

Sidney Burkett
Gregory Dame