Quantifiers (*, +, ?) in Bash Scripting - Mini Project: Build & Apply

Using Quantifiers (*, +, ?) in Bash Scripting

📖 Scenario: You are working on a bash script that processes a list of filenames. Some filenames have different patterns, and you want to filter them using regular expressions with quantifiers.Quantifiers like *, +, and ? help match patterns that repeat or appear optionally.

🎯 Goal: Build a bash script that uses grep with regular expressions containing quantifiers *, +, and ? to filter filenames based on specific patterns.

📋 What You'll Learn

Create a variable files containing a list of filenames separated by spaces.

Create a variable pattern_star with a regex using the * quantifier.

Use grep -E with pattern_star to filter filenames and save to result_star.

Print the filtered filenames stored in result_star.

💡 Why This Matters

🌍 Real World

Filtering and processing filenames or text data using regex patterns with quantifiers is common in scripting tasks like log analysis, file management, and automation.

💼 Career

Understanding regex quantifiers and using them in bash scripts is a valuable skill for system administrators, DevOps engineers, and automation specialists.

1

Create a list of filenames

Create a variable called files and assign it the exact string: file1.txt file22.txt file333.txt fileA.txt fileB.txt

Bash Scripting

# Create a variable called files with the exact filenames
# Your code here

Need a hint?

Use double quotes to assign the list of filenames as a single string to files.

2

Create a regex pattern with the * quantifier

Create a variable called pattern_star and assign it the regex string file[0-9]*\.txt which uses the * quantifier to match zero or more digits after 'file'.

Bash Scripting

files="file1.txt file22.txt file333.txt fileA.txt fileB.txt"
# Create a variable pattern_star with regex 'file[0-9]*\.txt'
# Your code here

Need a hint?

Remember to escape the dot . with a backslash \ in regex.

3

Filter filenames using grep with the * quantifier pattern

Use grep -E with the variable pattern_star to filter the filenames in files. Save the filtered filenames into a variable called result_star. Use echo and command substitution.

Bash Scripting

files="file1.txt file22.txt file333.txt fileA.txt fileB.txt"
pattern_star="file[0-9]*\.txt"
# Use grep -E with pattern_star to filter files and save to result_star
# Your code here

Need a hint?

Use grep -E -o to output only matching parts. Use $( ) for command substitution.

4

Print the filtered filenames

Print the variable result_star to display the filtered filenames.

Bash Scripting

files="file1.txt file22.txt file333.txt fileA.txt fileB.txt"
pattern_star="file[0-9]*\.txt"
result_star=$(echo "$files" | grep -E -o "$pattern_star")
# Print the filtered filenames stored in result_star
# Your code here

Need a hint?

Use echo "$result_star" to print the filtered filenames, each on a new line.