grep with regex (-E) in Linux CLI - Mini Project: Build & Apply

Using grep with Extended Regular Expressions (-E)

📖 Scenario: You work as a system administrator. You have a log file with many lines. You want to find lines that match certain patterns quickly.

🎯 Goal: Learn how to use grep -E to search for lines matching multiple patterns using extended regular expressions.

📋 What You'll Learn

Use the grep command with the -E option

Search for lines matching multiple patterns using the pipe | symbol

Use a sample text file with specific lines

Display the matching lines as output

💡 Why This Matters

🌍 Real World

System administrators often need to search logs quickly for errors or warnings to troubleshoot issues.

💼 Career

Knowing how to use grep with extended regex helps in filtering important information from large text files efficiently.

1

Create a sample log file

Create a file called log.txt with these exact lines:
error: disk full
warning: low memory
info: system rebooted
error: network down
info: user login

Linux CLI

# Create the file log.txt with the given lines
# Your code here

Need a hint?

Use echo -e with newline characters \n and redirect output to log.txt.

2

Set the search pattern variable

Create a variable called pattern and set it to the string "error|warning" to match lines containing either 'error' or 'warning'.

Linux CLI

echo -e "error: disk full\nwarning: low memory\ninfo: system rebooted\nerror: network down\ninfo: user login" > log.txt
# Create the variable pattern with value "error|warning"
# Your code here

Need a hint?

Use pattern="error|warning" to store the regex pattern.

3

Use grep with -E and the pattern variable

Use the command grep -E "$pattern" log.txt to search log.txt for lines matching the pattern stored in pattern.

Linux CLI

echo -e "error: disk full\nwarning: low memory\ninfo: system rebooted\nerror: network down\ninfo: user login" > log.txt
pattern="error|warning"
# Use grep -E with "$pattern" on log.txt
# Your code here

Need a hint?

Use grep -E "$pattern" log.txt to find matching lines.

4

Display the matching lines

Run the script to display all lines from log.txt that contain either 'error' or 'warning'.

Linux CLI

echo -e "error: disk full\nwarning: low memory\ninfo: system rebooted\nerror: network down\ninfo: user login" > log.txt
pattern="error|warning"
grep -E "$pattern" log.txt
# Run the command to show matching lines
# Your code here

Need a hint?

The output should show only lines with 'error' or 'warning'.