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.