SmallSh is a lightweight shell program for Linux written in C.

First, make sure you have git, make, and gcc installed on your system.

Navigate to the folder where you want to install the program and clone the repository with the command

git clone https://github.com/derthadams/SmallSh.git

then navigate inside the repository directory with

cd Smallsh

and compile the program with

make

Run the program with

smallsh

You should now see the SmallSh prompt in your terminal (a single colon):

:

From the SmallSh prompt you can launch any installed program or utility by typing its name.

For example, if you type

: ls

then ls will run and you'll see a listing of all files in the current directory:

README.md	makefile	smallsh		smallsh.c

To run a program in the background, use an ampersand (&) after the command. For example,

: sleep 5 &

will run the sleep utility for 5 seconds, but since it's running in the background it won't block SmallSh and you can run other commands while it's executing.

After you run a program in the background, SmallSh will display the pid for your reference:

background pid is 22418

If you want to stop the execution of a program running in the background, use kill with the program's pid:

: kill 22418

You'll then see the following message with the exit status code:

Background pid 22418 is done: exit value 0

If you want to check the exit status code of the most-recently terminated program, type

: status

and you'll get a message with the status code.

exit value 0

If the program exited without issues the code will be 0, but if an error occurred the code will be a different number.

For example, if you run the test utility with a filename argument that doesn't exist in the current directory

: test -f badfile

and then run the status command

: status

you'll get the message

exit value 1

test uses the exit status code to return a boolean value: 0 for true and 1 for false. Since badfile doesn't exist, the boolean result is false and the exit status code is 1.

If a program is terminated by a signal, SmallSh will display the signal number. For example, if you kill a process using CTRL-C, you'll see the message

terminated by signal 2

You can toggle foreground-only mode on and off using CTRL-Z. When SmallSh has has switched to foreground-only mode you'll see the message

Entering foreground-only mode (& is now ignored)

At this point, any ampersand (&) you include after a command will be ignored and the program will run in the foreground. When you want to switch back to normal mode, use CTRL-Z again and you'll see the message

Exiting foreground-only mode

SmallSh implements redirection of stdin and stdout using the < and > operators.

To redirect the output of a program to the input of a different program or to a file, use the > operator. For example, the command

: ls > myfile

will take the list of files and directories output by ls and save it to a text file called "myfile". If you then type

: cat myfile

you'll see the contents of myfile, which is just the output of ls with one row for each file or directory:

README.md
makefile
myfile
smallsh
smallsh.c

To redirect the input of a program, use the < operator. For example, the command

: wc < myfile

takes the contents of myfile and sends it as input to the wc (word count) utility. You should then see the output of wc:

       5       5      44

The results represent the number of lines (5), words (5), and characters (44) in the file.

SmallSh implements its own version of cd by calling the Linux API function chdir(). It works the same way as the built-in cd implementation.

Type cd, then provide a path for the directory you want to change to. For example,

cd ..

will change to the parent of the current directory.

To quit SmallSh, type

exit

To uninstall the SmallSh executable, use the command

make clean

You'll still have to manually delete the SmallSh folder with the source code, makefile, .gitignore and README.md.