Day 3: Linux Basic Commands

Commands-

To view what's written in a file.
```
 $ cat altos.txt
```
- cat -b: This adds line numbers to non-blank lines
- cat -n: This adds line numbers to all lines
- cat -s: This squeezes blank lines into one line
- cat –E: This shows $ at the end of the line
To run any bash script written in editors like nano,vim etc.
```
 ./altos.txt
```
- ./ - Allow you to run the bash script
To see all the permissions of files.
```
 ls -la
```
- ls - List files and directories
- -l - List files and directories with permission
- -a - List all files and directories, even hidden files and directories with permission

To change the access permissions of files.

 chmod 777 altos.txt

 chmod o+wx testfile

 ls -l testfile
 -rwxrwxrwx  1 amrood   users 1024  Nov 2 00:10  testfile

 chmod u-x testfile

 ls -l testfile
 -rw-rwxrwx  1 amrood   users 1024  Nov 2 00:10  testfile

 chmod g = rx testfile

 ls -l testfile
 -rw-r-xrwx  1 amrood   users 1024  Nov 2 00:10  testfile

Understanding Security Permissions
First, you need to think of the nine signs as three groups of three signs (see box below). Each of the three "rwx" icons represents a different action you can perform on the file.
```
  ---     ---     ---
  rwx     rwx     rwx
  user    group   other
```
r = “read” the file’s contents

w = “write”, or modify, the file’s contents

x = “execute” the file

- = "No permission"

To check which commands you have run till now.
```
 history
```
To make a file.
```
 touch file1.txt
```
To remove a file.
```
 rm file1.txt
```
To make a directory/folder.
```
 mkdir myfolder
```
To remove a directory/folder.
```
 mkdir -r myfolder
```

To create a fruits.txt file and to view the content.

touch fruits.txt 
echo "here is the watermelon" > fruits.txt | cat fruits.txt

touch fruits.txt 
vim fruits.txt
cat fruits.txt

Add content in devops.txt (One in each line) - Apple, Mango, Banana, Cherry, Kiwi, Orange, Guava.
```
vim fruits.txt
```
- vim - It is a text editor and after saving the edited file it'll automatically create the file without giving touch command.
  
  Below are the commands to use vim editor,
  
  Entering and Exiting Vim:
  - vim: Open a file in Vim.
  - vim filename: Open a specific file in Vim.
  - :q: Quit Vim.
  - :q!: Force quit Vim without saving changes.
  - :wq or :x: Save changes and exit Vim.
  - :w: Save changes to the current file.
  - :w filename: Save the file with a new name.
  - :wq or :x: Save changes and exit Vim.
```
  Apple 
  Mango
  Banana
  Cherry
  Kiwi
  Orange
  Guava

  # press "ESC + :wq + ENTER" to save and exit the file
```
To Show only top three fruits from the file.

The head command in Linux is used to display the first few lines of a text file. By default, it displays the first 10 lines of a file, but you can specify a different number of lines using the -n option. Here's the basic syntax of the head command:
```
head [OPTIONS] [FILE]
```
a) OPTIONS are optional flags that modify the behavior of the head command.

b) FILE is the name of the file you want to view. If not specified, head reads from standard input.

To display the first 3 fruits from fruits.txt file,
```
head -n 3 fruits.txt
```
To Show only the bottom three fruits from the file.

The tail command in Linux is used to display the last few lines of a text file. It is particularly useful for monitoring log files or any other text files where you want to see the most recent entries. Here's the basic syntax of the tail command:
```
tail [OPTIONS] [FILE]
```
a) OPTIONS are optional flags that modify the behavior of the tail command.

b) FILE is the name of the file you want to display. If not specified, tail reads from standard input.

To display the last 3 fruits from fruits.txt file,
```
tail -n 5 fruits.txt
```
To create another file colors.txt and to view the content.
```
touch colors.txt
```

Add content in colors.txt (One in each line) - Red, Pink, White, Black, Blue, Orange, Purple, Grey.

Red 
Pink
White 
Black 
Blue 
Orange 
Purple 
Grey

# Press "ESC + :wq + ENTER" to save and exit the file

To find the difference between fruits.txt and Colors.txt file.

The diff command compares two files line by line and highlights the differences. Here's the basic syntax:
```
diff fruits.txt colors.txt
```
or
```
vimdiff fruits.txt colors.txt #display the difference with visuals
```

Tara Prasad Sarangi

Tara Prasad Sarangi

Day 3: Linux Basic Commands

Commands-