Linux Basic commands and examples

ls:
- Description: The ls command is used to list files and directories in a directory.
- Syntax: ls [options] [file/directory]
- Example:
  - List all files and directories in the current directory:
```
  $ ls
  file1.txt  file2.txt  directory1
```
  - List files and directories in a specific directory:
```
  $ ls /path/to/directory
  file1.txt  file2.txt  directory1
```
cat:
- Description: The cat command is used to concatenate and display the contents of files.
- Syntax: cat [options] [file(s)]
- Example:
  - Display the contents of a file:
```
  $ cat filename.txt
  This is the contents of the file.
```
  - Concatenate multiple files and display their contents:
```
  $ cat file1.txt file2.txt
  Contents of file1.txt...
  Contents of file2.txt...
```
find:
- Description: The find command is used to search for files and directories based on specified criteria.
- Syntax: find [path] [expression]
- Example:
  - Find all files with a specific name in the current directory:
```
  $ find . -name "filename.txt"
  ./directory1/filename.txt
```
  - Find all directories modified in the last 7 days:
```
  $ find /path/to/directory -type d -mtime -7
  /path/to/directory/directory1
```

grep:

Description: The grep command is used to search for a specified pattern in files.
Syntax: grep [options] pattern [file(s)]

Example:

Search for a word in a file:

  $ grep "word" filename.txt
  This line contains the word.

Search for a pattern recursively in a directory:

  $ grep -r "pattern" /path/to/directory
  /path/to/directory/file1.txt: This line matches the pattern.
  /path/to/directory/file2.txt: Another line that matches the pattern.

cut:
- Description: The cut command is used to extract specific fields or columns from a file.
- Syntax: cut [options] [file(s)]
- Example:
  - Extract the first column from a CSV file:
```
  $ cut -d ',' -f 1 filename.csv
  Column1
  Data1
  Data2
```
  - Extract a range of characters from a file:
```
  $ cut -c 1-5 filename.txt
  This
  is
  a
  test
```
sort:
- Description: The sort command is used to sort lines of text in a file.
- Syntax: sort [options] [file(s)]
- Example:
  - Sort lines in a file in ascending order:
```
  $ sort filename.txt
  apple
  banana
  cherry
```
  - Sort lines numerically in descending order:
```
  $ sort -n -r numbers.txt
  100
  50
  10
```
echo:
- Description: The echo command is used to print arguments or text to the terminal.
- Syntax: echo [options] [text]
- Example:
  - Print a message to the terminal:
```
  $ echo "Hello, world!"
  Hello, world!
```
  - Print the value of a variable:
```
  $ variable="Value"
  $ echo $variable
  Value
```
head:
- Description: The head command is used to output the beginning lines of a file.
- Syntax: head [options] [file(s)]
- Example:
  - Display the first 10 lines of a file:
```
  $ head filename.txt
  Line 1
  Line 2
  Line 3
  ...
  Line 10
```
  - Display a specific number of lines from a file:
```
  $ head -n 5 filename.txt
  Line 1
  Line 2
  Line 3
  Line 4
  Line 5
```
tail:
- Description: The tail command is used to output the ending lines of a file.
- Syntax: tail [options] [file(s)]
- Example:
  - Display the last 10 lines of a file:
```
  $ tail filename.txt
  Line 91
  Line 92
  Line 93
  ...
  Line 100
```
  - Continuously display new lines added to a file:
```
  $ tail -f filename.log
  Line 1
  Line 2
  Line 3
  ... (new lines will be displayed in real-time)
```