Linux/Unix Commands

Listing Files

ls
If you want to see the list of files on your UNIX or Linux system, use the ls command
ls -l or ll
If you want to organize the files in list
ls -lh
If you want to arrange the files in list and show their size

Listing Hidden Files and Normal Files

ls -al
If you want ot see the list of all files with all hidden files in the Current directory system in Linux
ls -lha
If you want to organize files in list format with their sizes and see hidden files

-ls -l
-Displays long list view with detailed file information including file type, permissions, link count, owner, group, size, date and time

-ls -lt
-Lists all files sorted by date and time with the newest file first.

-ls -ltr
-Lists all files sorted by date and time with the oldest file first.

-ls -lh
-Displays all files in current directory with file sizes in human readable format(eg:1.6K,328M,2.4G)

-ls -a
-If you want to list all files including hidden files that start with "."

-ls -la
-Lists all files,including hidden files,in the current directory with detailed information.

-ls -F
-Displays all files in current directory with their file types.

Creating & Viewing Files

To create a new file, use the command
1. cat > filename
2. Add content
3. Press ctrl + d to return to command prompt.
Files can also be quickly created using
echo "Hello World" > ./fileName.txt
To view a file, use the command cat filename

Searching for content in a file/ files in a directory

To search for a word in a file using terminal,use the command grep
For eg., if you want to search for the word GNU in a file named GNU.txt,type grep GNU GNU.txt
This will show all lines which have the word GNU in that file
To search over multiple files in a directory, use grep with -r flag, like grep -r GNU .. Here -r stands for recursive search and . specifies the search root to be the current directory.

Searching for a file

find . -name ".js" -print: find all files with JS extnesion and print them on screen
find . -type d -name "*tmp" -print: print all directories ending with tmp
find . -type f -exec ls -l {} \;: use ls -l on all returned values

Exiting the shell

exit (also aliased to bye or quit in some shell flavors)

Get root access

To log in as a super user use one of the following commands in the terminal. You can actually use this command to log in as any user on the machine, but when left blank it will attempt to log in as root.\

su -
sudo -i
These commands will ask you for password.

To jump right into root, run\

sudo su -
Since there is no root password made after live install.

To run other commands as root temporarily, use the command\

sudo command
Replace the command above with your command. Eg: sudo apt-get update

Updating, Installing and Listing packages

The commands for installing and updating applications depend on the version of Linux you are using, specifically whether it's Debian- or RPM-based.

Debian Based systems
- Update the list of available packages and their versions, but doen not install or upgrade any packages. use the command sudo apt update
- Install newer versions of installed packages,use the command sudo apt upgrade
- Install any required package,use sudo apt install 'your package name'. Example: sudo apt install apache2
RPM-based systems
- Update all or specified packages,use sudo yum update. Example for updating specific package: sudo yum update mysql
- Lists known and installed packages,use sudo yum list sudo yum list --installed
- Install requested package,use yum install. Example: sudo yum -y install firefox

Download YouTube videos on Linux

For this you need to install an utility called youtube-dl, which is a command-line program to download videos from YouTube.com and a few more sites. It requires the Python interpreter, version 2.6, 2.7, or 3.2+, and it is not platform specific. It should work on your Unix box, on Windows or on macOS. It is open source project. You can contribute here.

To install it right away for all UNIX users (Linux, macOS, etc.), type:

sudo curl -L https://yt-dl.org/downloads/latest/youtube-dl -o /usr/local/bin/youtube-dl
sudo chmod a+rx /usr/local/bin/youtube-dl

If you do not have curl, you can alternatively use a recent wget:

sudo wget https://yt-dl.org/downloads/latest/youtube-dl -O /usr/local/bin/youtube-dl
sudo chmod a+rx /usr/local/bin/youtube-dl

It is very simple to use. Following are some example usages:

# simplest example
youtube-dl https://www.youtube.com/watch?v=Zuwa8zlfXSY

# customize the filename of the output
youtube-dl -o '%(title)s by %(uploader)s.%(ext)s' https://www.youtube.com/watch?v=Zuwa8zlfXSY

# download from multiple urls
youtube-dl <url1> <url2>

# or use a file with list of urls
youtube-dl -a url.txt

If you are more interested, there are plenty of other options to be explored from documentation page.

Shutting down the machine

shutdown -h now -If you want to Shutdown the system and turn the power off immediately.
shutdown -h +10 -If you want to Shutdown the system after 10 minutes.
shutdown -r now -If you want to Reboot the system using shutdown command.

Moving between Directories

Exploring cd(change directory) command

-cd [directory_name]
-If you want to change directory to a particular directory,use this command. Eg: cd Documents

-cd dir/subdir/subsubdir
-If you want to move inside a directory from a directory,use this command. Eg: cd Documents/Hacktoberfest/linuxCommands

-cd /
-If you want to change directory to the root directory. Root directory is the first directory in your file system hierarchy.

-cd ~ or cd
-If you want to change directory to the home directory.Generally known as $HOME,located at path /home//. Also, cd command can be used to do the same above operation.

-cd ..
-It is used to go one level back directory(i.e to parent directory of current directory).

-cd ../..
-It is used to go two levels back directory(i.e to parent's parent directory of current directory).

-cd -
-It is used to change back to the previous working directory. Eg: If Documents is present working directory and Downloads is previous working directory, this command takes you back to Downloads directory.

-cd "dir name" or cd dir\ name
-This command is used to navigate to a directory with white spaces.Instead of using double quotes we can use single quotes then also this command will work.Eg: cd "linux commands" or cd linux\ commands will move to 'linux commands' directory.

Compress files on linux

The following commands are used to compress files on linux. There are many ways to compress files in linux, the most common is tar

tar
- The following commands makes an archive named archive.tar containing file foo and bar present in the current directory.
- tar -cf archive.tar foo bar
- This command lists all the files in an archive verbosely.
- tar -tvf archive.tar
- The tar utility has many options which can be seen using
- tar --help
Basic Commands

wc
- One of the most basic commands, wc allows the user to count the number of bytes, characters, words and lines of each given file or standard input and print the result.
- Basic Use:
Syntax:
```
$ wc filename  # output: number_of_lines number_of_words number_of_characters /path/to/file
```
Example:
```
$ wc /proc/cpuinfo  # output: 208 1232 6336 /proc/cpuinfo
```
touch
- touch is a simple command that allows the user to create an empty file. Note that with touch, you can only create the file and not edit it.
- Basic Use:
Syntax:
```
$ touch filename
$ ls -l filename
-rw-rw-rw- 1 current_user users 0 Oct  9 22:03 filename
```
Example: Logged in as user linux_is_awesome
```
$ touch hello
$ ls -l hello
-rw-rw-rw- 1 linux_is_awesome users 0 Oct  9 22:03 hello
```
whoami
- whoami command displays the username of the current user.
- Basic Use:
Syntax:
```
$ whoami
current_user
```
Example: Logged in as user linux_is_awesome
```
$ whoami
linux_is_awesome
```
grep
- grep is an extremely useful command to know in Linux.
- It stands for “global regular expression print". Basically, it's used for pattern matching. grep processes text line by line and prints any lines which match a specified pattern.
- Basic Use:
Syntax:
```
$ grep [option(s)] pattern [file(s)]
```
Creating a test file for using grep:
```
$  cat > grep_test.txt
This is a test file. AAA, BBB, 123, CaSe ExAmPle.
```
Example:
```
$ grep AAA grep_test.txt
This is a test file. AAA, BBB, 123, CaSe ExAmPle. # AAA will be highlighted in the output

$ grep -i case grep_test.txt  # ignore case while searching
This is a test file. AAA, BBB, 123, CaSe ExAmPle. # CaSe will be highlighted in the output
```

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Linux/Unix Commands

Listing Files

Listing Hidden Files and Normal Files

Creating & Viewing Files

Searching for content in a file/ files in a directory

Searching for a file

Exiting the shell

Get root access

Updating, Installing and Listing packages

Download YouTube videos on Linux

Shutting down the machine

Moving between Directories

Compress files on linux

Basic Commands

`wc`

`touch`

`whoami`

`grep`

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Linux/Unix Commands

Listing Files

Listing Hidden Files and Normal Files

Creating & Viewing Files

Searching for content in a file/ files in a directory

Searching for a file

Exiting the shell

Get root access

Updating, Installing and Listing packages

Download YouTube videos on Linux

Shutting down the machine

Moving between Directories

Compress files on linux

Basic Commands

wc

touch

whoami

grep

`wc`

`touch`

`whoami`

`grep`