Introduction to Linux Command Line

Whenever it comes to some serious stuff like using a cluster or open-source software like OpenFOAM people are faced with the famous Linux command line. It was scary at the first sight but later on, when you get used to him, he will be your best friend.

Here some basic commands that it as a good start point

When you open a terminal you might only see a blinking cursor

If you type pwd, this will give you your current working directory’s absolute path

Here my current terminal output

pwd
/home/kursayurt

Now I know that I am on my home directory. I want to know which files or directories inside this directory. Simply typing ls is gives you that ones

ls
 Blog
 Desktop
 Documents
 Downloads
 hello.cpp
 Pictures
 Project
 Public
 Templates
 TUM
 Videos
 yd

As you see here is a hello.cpp file and some other directories are around here

Let’s go to my Desktop directory using cd command

cd Desktop
pwd
/home/kursatyurt/Desktop

Now as you see I have changed the current directory to my Desktop

ls
Ch8Sub.pdf               worksheet2.pdf
cfdlab-lecture-notes.pdf
ws-navier-stokes.pdf

There is pdf files around. If I want to open one of them I can simply open them using xdg-open command which is open any type of file using default software defined by the system

xdg-open woorksheet2.pdf

To go back we can type

cd ..
pwd
/home/kursatyurt

This take us one directory back.

Now if I want to copy a file from my Desktop to Home directory, I can follow this thing.

cp ./Desktop/worksheet2.pdf .

Here cp command takes two arguments first one is the source and the second one is the destination

./ denotes from current directory by this way we can espace from writing absolute path. Also in the second argument . means here.

If we want to move a folder or file we use mv command which is similar to cp, one important thing about copy is you cannot copy a folder using cp command alone you need to give recursive flag -r

cp -r /source/directory /destination/directory

By this way one can copy a folder.

In order to create a new directory, we are using mkdir command

mkdir directoryname

This creates a new directory under our current directory as like any other linux command we can do operation other than our current directory giving absolute path

mkdir /absolute/path/to/directory

Now take a look at removing files/directories. An important thing about removing is that this operation is irreversible, no Trash Bin deleted files from command line goes.

Let’s first look into deleting files

rm FileName

Removing directories are requires a recursive operation

rm -r DirectoryName

One other important thing is of course when you are doing an operation or running a program you might want to cancel that process. For this purpose [Control]+c is used.