What is Linux?
The era of computing has come a long way, starting from the punched card to today’s cloud platforms, a significant progress has been made. We are now habituated in using such cloud platforms. The most popular example can be Google’s Colab, which has made cloud computing available publicly. If you have ever used Google’s Colab, you are probably familiar with Linux.
Linux is the community driven operating system based on something called Linux Kernel which empowers devices starting from smart phones to large cloud servers. So, the fact is knowingly or unknowingly we are using devices in our daily lives which are powered by Linux Kernel.
The linux kernel was first developed by Linus Torvald in 1991 as a personal hobby project and later it was made available publicly. You can refer to this article to know more on this.
In this post, I will be sharing some basic to intermediate linux commands which will help you to start your journey with linux based systems, may be on your personal computer or on a cloud platform.
disclaimer: I will be using a rendering engine called Quarto to develop this post as a GitHub flavored markdown and it needs Python to run bash commands, this is why there is ! right before the actual bash command everywhere. ! should not be considered as a part of any of the bash commands that will be used here unless I explicitly mention.
Tools to communicate with linux based systems
In any form of linux based systems, the most basic tool to interact with is the command line application a.k.a Terminals or Console, which is nothing but an application equivalent to cmd on Windows, but much more powerful than it. It is the application which accepts commands from the user and performs the instructions accordingly.
Now, there is one more thing working behind the scene that is called shell. Shell is the engine which parses or interprets the commands given by the user. There are different types of shell. Typically, it is the bash shell where bash stands for Bourne Again SHell. Other shell applications available are ZShell or Fish (Friendly Interactive Shell).
I will be runnning the commands using bash shell.
Task specific commands
If you open the terminal anytime, typically you would see a prompt ending with :~$ and the cursor blinking next to it. It is now ready for accepting commands from the user. The terminal usually points to a directory on the system which, by default, is the user’s home directory (i.e. the path /home/<user>/), which can be reconfigured to point to a different location based on our need.
Getting the basic information
👉 The whoami command
whoami is a command that returns the user name currently logged in.
koushik👉 The date command
date gives you the current date and time.
Wed Mar 22 17:23:23 IST 2023👉 The pwd command
pwd stands for the present working directory which is pointed out by the terminal. For me the pwd is /home/koushik/
/home/koushik/quarto-docs👉 The ls command
ls stands for listing, which returns names of all the files and directories (folders) availble inside the pwd.
bash-commands-for-cloud.ipynb koushik.txt records.txt
bash-commands-for-cloud.md my_first_file.txt test_dir
bash-commands-for-cloud.qmd my_second_file.txtNote that ls only returns the names of files and directories which are not hidden, this is the default behavior of ls, if you want to see something more you need some other options while using it, which are often called flags.
I will use some flags below and try to explain what they mean.
different flags of ls
. bash-commands-for-cloud.qmd records.txt
.. koushik.txt test_dir
bash-commands-for-cloud.ipynb my_first_file.txt
bash-commands-for-cloud.md my_second_file.txt-a flag is used for showing all the files and directories within pwd including hidden ones. In linux hidden files are directories have . in their names at the the very beginning.
bash-commands-for-cloud.ipynb koushik.txt records.txt
bash-commands-for-cloud.md my_first_file.txt test_dir
bash-commands-for-cloud.qmd my_second_file.txt-h flag is used for better representation for the users (human being, that’s why h)
total 68
-rw-r--r-- 1 koushik koushik 16787 Mar 22 17:23 bash-commands-for-cloud.ipynb
-rw-r--r-- 1 koushik koushik 17507 Mar 22 17:13 bash-commands-for-cloud.md
-rw-r--r-- 1 koushik koushik 9697 Mar 22 17:23 bash-commands-for-cloud.qmd
-rw-r--r-- 1 koushik koushik 58 Mar 22 12:58 koushik.txt
-rw-r--r-- 1 koushik koushik 0 Mar 22 17:13 my_first_file.txt
-rw-r--r-- 1 koushik koushik 58 Mar 22 12:49 my_second_file.txt
-rw-r--r-- 1 koushik koushik 87 Mar 22 17:13 records.txt
drwxr-xr-x 2 koushik koushik 4096 Mar 22 17:12 test_dir-l flag is used for showing entries in a long format
bash-commands-for-cloud.ipynb records.txt koushik.txt
bash-commands-for-cloud.qmd my_first_file.txt my_second_file.txt
bash-commands-for-cloud.md test_dir-t flag is used for showing entries sorted based on when they are created
total 68
20 bash-commands-for-cloud.ipynb 4 koushik.txt 4 records.txt
20 bash-commands-for-cloud.md 0 my_first_file.txt 4 test_dir
12 bash-commands-for-cloud.qmd 4 my_second_file.txt-s flag is used for showing the allocated sizes of the files
You can definitely combine multiple flags together just by putting them next to each other like below and obviously you will get the combined effect of them
total 76K
20K -rw-r--r-- 1 koushik koushik 17K Mar 22 17:23 bash-commands-for-cloud.ipynb
4.0K drwxr-xr-x 3 koushik koushik 4.0K Mar 22 17:23 .
12K -rw-r--r-- 1 koushik koushik 9.5K Mar 22 17:23 bash-commands-for-cloud.qmd
20K -rw-r--r-- 1 koushik koushik 18K Mar 22 17:13 bash-commands-for-cloud.md
4.0K -rw-r--r-- 1 koushik koushik 87 Mar 22 17:13 records.txt
0 -rw-r--r-- 1 koushik koushik 0 Mar 22 17:13 my_first_file.txt
4.0K drwxr-xr-x 2 koushik koushik 4.0K Mar 22 17:12 test_dir
4.0K -rw-r--r-- 1 koushik koushik 58 Mar 22 12:58 koushik.txt
4.0K -rw-r--r-- 1 koushik koushik 58 Mar 22 12:49 my_second_file.txt
4.0K drwxr-xr-x 14 koushik koushik 4.0K Mar 22 12:39 ..One more thing to note here is that, you can use ls to see the contents of any directory just by putting the path next to ls call followed by a space character like below
total 2.0M
4.0K drwxrwxrwt 8 root root 4.0K Mar 22 17:23 tmp
4.0K drwxr-xr-x 80 root root 4.0K Mar 22 10:44 etc
4.0K drwxr-xr-x 4 root root 4.0K Mar 22 10:44 opt
4.0K drwx------ 3 root root 4.0K Mar 22 10:44 root
0 drwxr-xr-x 7 root root 140 Mar 22 08:52 run
4.0K drwxr-xr-x 19 root root 4.0K Mar 22 08:50 .
4.0K drwxr-xr-x 19 root root 4.0K Mar 22 08:50 ..
0 drwxr-xr-x 11 root root 3.0K Mar 22 08:50 dev
0 dr-xr-xr-x 202 root root 0 Mar 22 08:50 proc
0 dr-xr-xr-x 11 root root 0 Mar 22 08:50 sys
4.0K drwxr-xr-x 3 root root 4.0K Mar 20 19:58 home
4.0K drwxr-xr-x 5 root root 4.0K Mar 20 19:57 mnt
16K drwx------ 2 root root 16K Mar 20 19:57 lost+found
4.0K drwxr-xr-x 8 root root 4.0K Feb 11 03:06 snap
4.0K drwxr-xr-x 13 root root 4.0K Feb 11 03:06 var
4.0K drwxr-xr-x 14 root root 4.0K Feb 11 03:05 usr
4.0K drwxr-xr-x 2 root root 4.0K Feb 11 03:05 media
4.0K drwxr-xr-x 2 root root 4.0K Feb 11 03:05 srv
0 lrwxrwxrwx 1 root root 7 Feb 11 03:05 lib -> usr/lib
0 lrwxrwxrwx 1 root root 9 Feb 11 03:05 lib32 -> usr/lib32
0 lrwxrwxrwx 1 root root 9 Feb 11 03:05 lib64 -> usr/lib64
0 lrwxrwxrwx 1 root root 10 Feb 11 03:05 libx32 -> usr/libx32
0 lrwxrwxrwx 1 root root 8 Feb 11 03:05 sbin -> usr/sbin
0 lrwxrwxrwx 1 root root 7 Feb 11 03:05 bin -> usr/bin
4.0K drwxr-xr-x 2 root root 4.0K Apr 18 2022 boot
1.9M -rwxrwxrwx 1 root root 1.9M Jan 1 1970 initHere ls is showing the contents of a special directory a.k.a root, this is equivalent to the C:\ drive on Windows.
👉 The echo command
echo evaluates an expression and prints that on the terminal.
Wed Mar 22 17:23:24 IST 2023here date is evaluated by echo and the output of echo is printed on the terminal (or console).
Here is another example of echo.
Julia claims to be faster that Pythonthere are two things to note here:
- we are creating a shell variable called
namewith the valueJuliaand this variable is referred in theechocall to print a formatted string on the console - creation of
nameand callingechoare two separate commands which are being executed in a sequence by using&&operator. The\is used for breaking the lines to make the command flow through multiple lines.
Working with files and directories
Now, you know the basics of running commands and getting some simple yet useful information, it is the time to see a bit more interesting commands.
👉 Creating a file with touch
touch creates a file with the name given by the user right next to it followed by a space character.
👉 Writing data to a file using tee
# writing date to file, the file will be created if it does not exist
!date | tee records.txt
# writing data in append mode with flag '-a'
!date | tee -a records.txt
# evaluate and then write in append mode
!echo $(date) | tee -a records.txtWed Mar 22 17:23:25 IST 2023
Wed Mar 22 17:23:25 IST 2023
Wed Mar 22 17:23:25 IST 2023By default, tee overwrites the data to the file, -a is used to avoid this.
We have one more operator (|) here, it is called pipe operator. It takes the output of the previous command and passes to the next command.
Writing same data to multiple files is also very intuitive as in date | tee -a file1.txt file2.txt file3.txt
The same operations can also be performed using redirect operator >. date > record.txt will write the system date time by overrwriting the file and date >> record.txt will write the data to the file in append mode.
A file can be removed using the rm command, e.g. rm record.txt
👉 Working with directory (folder)
# create directory with 'mkdir'
!mkdir test_dir_1
!mkdir test_dir_2
# create directory recussively along a path with flag '-p'
!mkdir -p test_dir_1/sub_dir/sub_sub_dir
# remove directories with 'rm'
!rm -d test_dir_2 # '-d' flag (directory) is used to remove an empty directory
!rm -r test_dir_1 # '-r' flag (recurive) is used to remove a directory and all of its contents
# rm -rf test_dir_1 '-f' flag (force) is used to remove a directory and all of its contents forcefullymultiple directories can also be removed just by specifying their paths one by one. One very useful flag for rm command is -i, which makes the removal process interactive.
Note: In linux, if you add a . before the file and diretory name, then it will be hidden which means simple ls command cannot show you these, you must to use ls -a to locate them 😉 .
👉 Copying files and directories from source to destination
To copy a file or directory from source to destination, we have the command cp. See the examples below to understand how it works,
- copy a file:
cp source_path/file.txt destination_path/ - copy a directory:
cp -r source_path/test_dir/ destination_path/
👉 Searching for files and directories using grep
Sometimes you may need a search for a file or directory inside the terminal. This can be done using the command called grep. It is used with ls through a pipe operator as if we are telling bash to filter the ls output by the pattern. See the examples below,
0 -rw-r--r-- 1 koushik koushik 0 Mar 22 17:23 my_first_file.txt👉 Editing a file with nano
nano is a text editor which typically available in almost all linux based systems. It is very useful if you quickly want to edit a file without leaving the terminal.
nano <your_file_name> is the command to open a file with nano. Once you are done with the editing, you can use Ctrl+S (Cmd+S in case you’re using clound from a Mac) to save the file and Ctrl+X (or Cmd+X in Mac) to close the editor.
👉 Viewing the content of a file using cat
In case you want to see the content of a file, you have a command called cat. It has several flags to use based on your requirements. Be careful, when using cat for a large file, by default it will show you everything that is there in the file.
Wed Mar 22 17:23:25 IST 2023
Wed Mar 22 17:23:25 IST 2023
Wed Mar 22 17:23:25 IST 2023You can use the flag -n to see the line numbers right before the lines.
1 Wed Mar 22 17:23:25 IST 2023
2 Wed Mar 22 17:23:25 IST 2023
3 Wed Mar 22 17:23:25 IST 2023That’s all for the part 1. I hope you have enjoyed reading the post, stay tuned for the next part.