Day 1

Advanced Linux Commands, Piping, Redirection, and Bash Scripting

1.1 Advanced Linux Commands

These commands help automate tasks and manage system operations more efficiently.

• grep: Search for patterns in files.

  • Example: grep "pattern" filename → Finds the word "pattern" in the file.

• find: Locate files and directories.

  • Example: find /home -name "file.txt" → Find file.txt in /home.

• tar: Archive and extract files.

  • Example:
    • Archive: tar -cvf archive.tar file1 file2
    • Extract: tar -xvf archive.tar

• awk: Text processing in files.

  • Example: awk '{print $1}' file.txt → Prints the first column.

• sed: Stream editor for text substitution.

  • Example: sed 's/old/new/' file.txt → Replaces "old" with "new" in the file.

• top / htop: Display system processes.

  • Use htop for a user-friendly, colorful interface.

1.2 Piping and Redirection

Piping (|)

Pass the output of one command as input to another.

• Example: ls -l | grep ".txt" → List only .txt files.

Redirection

Send output or input to/from files:

• >: Overwrite output to a file
  • Example: echo "Hello" > file.txt → Writes "Hello" to file.txt.
• >>: Append output to a file
  • Example: echo "World" >> file.txt → Adds "World" to file.txt.
• <: Input redirection
  • Example: sort < file.txt → Sorts the contents of file.txt.

1.3 Introduction to Bash Scripting

What is Bash Scripting?

Automating repetitive tasks in Linux. Bash scripts are sequences of Linux commands stored in a file.

Creating a Bash Script

1. Open a file: nano script.sh
2. Add the shebang:

   #!/bin/bash
   echo "Hello, World!"
3. Save and close the file.
4. Make it executable: chmod +x script.sh
5. Run the script: ./script.sh

Variables in Bash

#!/bin/bash
name="CyberTeam"
echo "Welcome to $name's Masterclass!"

Conditionals

#!/bin/bash
if [ -f "file.txt" ]; then
    echo "File exists"
else
    echo "File does not exist"
fi

Loops

#!/bin/bash
for i in {1..5}; do
    echo "Number $i"
done

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