Linux Commands

Linux is an open-source Unix operating system based on the Linux Kernel. The Linux commands are useful for operating the Linux operating system. All basic and advanced tasks can be done by executing commands. The commands are executed on the Linux terminal, It’s similar to the Command Prompt application in Windows. Keep in mind that all Linux commands are case-sensitive.

Commands

Navigate to the command that you want to learn.

pwd	cd	ls	mkdir	rm	rmdir	touch	cat

pwd
- pwd stands for Print Working Director.
- It prints the full pathname of the current working directory starting from the root.
Syntax:
```
$ pwd
```
Example:
```
teja@LAPTOP:Users/Teja$ pwd
Users/Teja
```
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cd
- cd stands for Change Directory.
- Used to change the current working directory. We can move all over our directories in our system.
1. To navigate to a directory from the root directory -
```
$ cd [/Root_Name/Destination_Path]
```
```
teja@LAPTOP:/mnt/c$ cd /mnt/c/Users/Teja
teja@LAPTOP:/mnt/c/Users/Teja$
```
2. To navigate to next directory(sub-directory) -
```
$ cd [SubDirectory_Name]
```
```
teja@LAPTOP:Users/Teja$ cd Desktop
teja@LAPTOP:Users/Teja/Desktop$
```
3. To navigate to the previous directory(the parent directory of the current directory) -
```
$ cd ..
```
```
teja@LAPTOP:Users/Teja/Desktop$ cd ..
teja@LAPTOP:Users/Teja$
```
4. To navigate to the root directory -
- The root directory is the first directory in our filesystem.
```
$ cd /
```
```
teja@LAPTOP:Users/Teja/Desktop$ cd /
teja@LAPTOP:/$
```
5. To navigate to the home directory -
```
$ cd ~
```
```
teja@LAPTOP:Users/Teja/Desktop$ cd ~
teja@LAPTOP:~$
```
```
$ cd
```
- This above command also works as cd ~
6. To navigate to a directory with spaces in the directory name -
```
$ cd ["Dictory_Name"]
```
```
teja@LAPTOP:Users/Teja$ cd "App Data"
teja@LAPTOP:Users/Teja/App Data$
```
- We can use single quotes instead of double quotes, cd 'App Data'
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ls
- ls command is known for listing files or directories which are present in a directory.
Syntax:
```
$ ls
```
Example:

1. List files or content in the present working directory -
```
teja@LAPTOP:Users/Teja$ ls
Desktop       Music       Games
Documents     Pictures   Videos
Downloads   
```
2. List files in another working directory -

Syntax:
```
$ls [Directory_Name] 
```
```
teja@LAPTOP:Users/Teja$ ls Desktop
Brave.lnk  'Microsoft Edge.lnk'  'Sublime Text.lnk'  'Visual Studio Code.lnk'
```
3. Type the ls / command to list the contents of the root directory.
4. Type the ls .. command to list the contents of the parent directory one level above. Use ls ../.. for contents two levels above.
5. Type the ls ~ command to list the contents in the users' home directory.
6. Type the ls -d */ command to list only directories.
7. Type the ls * command to list the contents of the directory with its subdirectories.
8. Type the ls -s command (the s is lowercase) to list files or directories with their sizes.
9. Type the ls -l command to list the contents of the directory in a table format with columns including.
```
teja@LAPTOP:Users/Teja$ ls -l
drwxrwxrwx 1 teja teja    4096 Nov 25 14:51  Desktop
drwxrwxrwx 1 teja teja    4096 Nov 25 18:39  Documents
drwxrwxrwx 1 teja teja    4096 Nov 25 20:39  Downloads
drwxrwxrwx 1 teja teja    4096 Nov 27  2021  Music
drwxrwxrwx 1 teja teja    4096 Oct 28 20:02  Pictures
drwxrwxrwx 1 teja teja    4096 Nov 27  2021  Games
drwxrwxrwx 1 teja teja    4096 Nov 19 22:24  Videos
```
10. Type the ls -lh command to list the files or directories in the same table format above, but with another column representing the size of each file/directory.
```
teja@LAPTOP:Users/Teja$ ls -lh
drwxrwxrwx 1 teja teja 4.0K Nov 25 14:51  Desktop
drwxrwxrwx 1 teja teja 4.0K Nov 25 18:39  Documents
drwxrwxrwx 1 teja teja 4.0K Nov 25 20:39  Downloads
drwxrwxrwx 1 teja teja 4.0K Nov 27  2021  Music
drwxrwxrwx 1 teja teja 4.0K Oct 28 20:02  Pictures
drwxrwxrwx 1 teja teja 4.0K Nov 27  2021  Games
drwxrwxrwx 1 teja teja 4.0K Nov 19 22:24  Videos
```
11. Type the ls -a command to list files or directories including hidden files or directories'. In Linux, anything that begins with a .is considered a hidden file`
```
teja@LAPTOP:Users/Teja$ ls -a
.bash_history        Desktop      Music       Games
.gitconfig           Documents    Pictures    Videos
.lesshst             Downloads
.minttyrc            
.node_repl_history
```
12. Type the ls -t command to list files or directories and sort by last modified date in descending order (biggest to smallest).
- You can also add a -r flag to reverse the sorting order like so: ls -tr
13. Type the ls -S (the S is uppercase) command to list files or directories and sort by size in descending order (biggest to smallest).
- You can also add a -r flag to reverse the sorting order like so: ls -Sr
14. Type the ls > [File_Name].txt command to print the output of the preceding command into an File_Name.txt file.
- You can use the file as you see fit, or log the contents of the file with cat File_Name.txt
```
teja@LAPTOP:Users/Teja$ ls > file.txt
teja@LAPTOP:Users/Teja$ cat file.txt
Desktop
Music
Games
Documents
Pictures
Videos
Downloads
```
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mkdir

mkdir command is used to create new directories.
This command can create multiple directories at once as well as set the permissions for the directories.

Syntax:

$ mkdir [Directory_Name]

Example:

teja@LAPTOP:Users/Teja/Games$ ls
Action
teja@LAPTOP:Users/Teja/Games$ mkdir Adventure
teja@LAPTOP:Users/Teja/Games$ ls
Action     Adventure

-v flag will prints a message for each created directory.

$ mkdir -v [Directory_Name]

We can create multiple directories at a time by mkdir [Dir1] [Dir2] [Dir3]
We can create sub-directories also by using -p flag.

$ mkdir -p [dir1_nanme/dir2_name/dir3_name]

teja@LAPTOP:Users/Teja$ mkdir -p dir1/dir2/dir3
teja@LAPTOP:Users/Teja$ ls
dir1
teja@LAPTOP:Users/Teja$ cd dir1
teja@LAPTOP:Users/Teja/dir1$ ls
dir2
teja@LAPTOP:Users/Teja/dir1$ cd dir2
teja@LAPTOP:Users/Teja/dir1/dir2$ ls
dir3

-m sets the file permissions. For instance, to create a directory with full read, write, and execute permissions for all users.

$ mkdir -m777 [directory_name]

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rm
- rm command is used to delete files and folders(directories).
Syntax:
```
$ rm [File or Directory]
```
Example:
```
teja@LAPTOP:Users/Teja$ ls
file1.txt      file2.txt     file3.txt
teja@LAPTOP:Users/Teja$ rm file1.txt
teja@LAPTOP:Users/Teja$ ls
file2.txt     file3.txt
```
- -i option makes the command ask the user for confirmation before removing each file. rm -i file1.txt.
- -f (force deletion) option overrides write protected and removes the file forcefully.
- We can delete multiple files at a time by rm file1.txt file2.txt file3.txt.
- Deleting directories -
- -d option will remove empty directories.
```
$ rm -d [Directory_Name]
```
- -d option can't delete non-empty directories.
- -r option removes all the files and sub-directories (non-empty directories) in the parent directory.
```
teja@LAPTOP:Users/Teja$ ls
Desktop       Music       Games
teja@LAPTOP:Users/Teja$ rm -r Games
teja@LAPTOP:Users/Teja$ ls
Desktop       Music
```
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rmdir
- rmdir command is used to delete an empty directory permanently.
Syntax:
```
$ rmdir [Directory_Name]
```
Example:
```
teja@LAPTOP:Users/Teja$ ls
Desktop       Music       Games
teja@LAPTOP:Users/Teja$ rmdir Games
teja@LAPTOP:Users/Teja$ ls
Desktop       Music
```
- rmdir can't delete a directory if it's not empty. For that we have to use rm -r command.
- -p works for deleting a subdirectory and its parent directory.
```
$ rmdir -p /Directory/SubDirectory
```
- -v option will print a text as a confirmation that the specified directory has been deleted.
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touch

touch command is used to create empty files, and change the timestamps of files or folders.

Syntax:

$ touch [File_Name]

Example:

teja@LAPTOP:Users/Teja$ ls
teja@LAPTOP:Users/Teja$ touch file.txt
teja@LAPTOP:Users/Teja$ ls
file.txt

We can create multiple files at a time by touch file1.txt file2.txt file3.txt.
We can auto-generate file names using curl braces while creating multiple files like in the following example:

$ touch file_name{1..3}.txt
$ ls
file_name1.txt    file_name2.txt    file_name3.txt

-a option will change the access time of a file to the current time.

@teja$ stat file.txt
Access: (0777/-rwxrwxrwx)  Uid: ( 1000/    teja)   Gid: ( 1000/    teja)
Access: 2022-11-27 16:55:19.142152800 +0530
Modify: 2022-11-27 16:53:31.937936000 +0530
Change: 2022-11-27 16:55:18.013885600 +0530
@teja$ touch -a file.txt
Access: (0777/-rwxrwxrwx)  Uid: ( 1000/    teja)   Gid: ( 1000/    teja)
Access: 2022-11-27 17:00:19.142152800 +0530
Modify: 2022-11-27 16:53:31.937936000 +0530
Change: 2022-11-27 17:00:18.013885600 +0530

-m option will change the modification time only. This will update the last modification time.

$ touch -m [File_Name]

@teja$ stat file.txt
Access: (0777/-rwxrwxrwx)  Uid: ( 1000/    teja)   Gid: ( 1000/    teja)
Access: 2022-11-27 17:00:19.142152800 +0530
Modify: 2022-11-27 16:53:31.937936000 +0530
Change: 2022-11-27 17:00:18.013885600 +0530

@teja$ touch -m file.txt
Access: (0777/-rwxrwxrwx)  Uid: ( 1000/    teja)   Gid: ( 1000/    teja)
Access: 2022-11-27 17:15:25.142152800 +0530
Modify: 2022-11-27 17:15:25.937936000 +0530
Change: 2022-11-27 17:15:25.013885600 +0530

-am option will change the both access time and modification time.
-r option is used to use the timestamp of another file. This means It will set the access and modification time of a file by reading the timestamp information from another file.

$ touch -r [reference_file_name] [file_name]

-d option is used to specify date and time as a string.

@teja$ touch -d '28 feb' file.txt
@teja$ ls -l
-rwxrwxrwx 1 teja teja      0 Feb 28  2022  file.txt

Instead of date we can specify time. This will update the current date.

@teja$ touch -d '10:30' file.txt
@teja$ ls -l
-rwxrwxrwx 1 teja teja      0 Nov 27  10:30  file.txt

-t option can update both the date and time that we mention in a specified format.

$ touch -t YYMMDDHHMM [file_name]

@teja$ touch -t 200202281030 file.txt
@teja$ ls -l
-rwxrwxrwx 1 teja teja      0 Feb 28  2002  file.txt

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cat
- cat command is used to display the content of a file. It helps us to create, view, and 'concatenate files.
Syntax:
```
$ cat [option] [file_name]
```
Example:
```
@teja$ ls
file.txt
@teja$ cat file.txt
Welcome to Linux Commands
```
- We can open multiple files by cat file1.txt file2.txt file3.txt. This will display the information of all three files.
- -n will display the contents of a file preceding line numbers.
```
@teja$ cat -n file.txt
1 Hello
2 How are you
3 Good to see you
```
- > option will create a file. The terminal will wait for the input text and store it in that file.
```
@teja$ cat > file.txt
```
- It will copy the contents of one file to another file.
```
$ cat [filename-whose-contents-is-to-be-copied] > [destination-filename]
```
- It will append the contents of one file to the end of another file.
```
$ cat file1 >> file2
```
- tac will display the content in reverse order.
```
@teja$ tac file.txt
olleH
```
- -E option will highlight the end of the line.
```
@teja$ cat -E file.txt
Hello$
How are you$
Good to see you$
```
- -- option will open dashed files.
```
$ cat -- "-dashfile"
```
- If the file has a lot of content and can’t fit in the terminal.
- | more will help.
```
$ cat file.txt | more
```
- It will merge the contents of multiple files.
```
$ cat "filename1" "filename2" "filename3" > "merged_filename"
```
- *.txt option will display all the text files in the folder.
```
$ cat *.txt
```
- >> will write in an existing file. The terminal will wait for the input text and store it at the end.
```
$ cat >> file.txt
Newly added text 
```
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Linux Commands

Commands

pwd

Syntax:

Example:

cd

ls

Syntax:

Example:

Syntax:

mkdir

Syntax:

Example:

rm

Syntax:

Example:

rmdir

Syntax:

Example:

touch

Syntax:

Example:

cat

Syntax:

Example:

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Linux Commands

Commands

pwd

Syntax:

Example:

cd

ls

Syntax:

Example:

Syntax:

mkdir

Syntax:

Example:

rm

Syntax:

Example:

rmdir

Syntax:

Example:

touch

Syntax:

Example:

cat

Syntax:

Example:

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