[[ ]] extended test in Bash Scripting - Mini Project: Build & Apply

Extended test

📖 Scenario: You are writing a bash script that needs to check multiple conditions on strings and files. The basic test command [ ] has limitations, so you want to use the extended test [[ ]] which supports pattern matching, regex, and logical operators without quoting issues.

🎯 Goal: Build a bash script that uses [[ ]] extended test for string comparison, pattern matching, and combining conditions with logical operators.

📋 What You'll Learn

Use [[ ]] for string comparison

Use [[ ]] with pattern matching using == and wildcards

Use [[ ]] with regex matching using =~

Combine multiple conditions using && and || inside [[ ]]

💡 Why This Matters

🌍 Real World

Extended tests are used in production bash scripts to safely check strings, validate input formats, and combine conditions without worrying about word splitting or globbing issues.

💼 Career

Understanding <code>[[ ]]</code> vs <code>[ ]</code> is a common interview question and essential for writing robust shell scripts in DevOps and system administration roles.

1

Basic string comparison with extended test

Create a variable called lang set to bash. Use [[ ]] to check if lang equals bash and print Match found if true.

Bash Scripting

# Set variable lang to 'bash'
# Use [[ ]] to compare and print 'Match found'
# Your code here

Need a hint?

Use [[ "$lang" == "bash" ]] for string comparison inside extended test.

2

Pattern matching with wildcards

Create a variable called filename set to report.txt. Use [[ ]] with a wildcard pattern to check if filename ends with .txt and print Text file detected if true.

Bash Scripting

lang="bash"
if [[ "$lang" == "bash" ]]; then
  echo "Match found"
fi
# Set filename and check if it ends with .txt using wildcard
# Your code here

Need a hint?

Use [[ "$filename" == *.txt ]] — the wildcard must not be quoted on the right side.

3

Regex matching with =~

Create a variable called email set to [e-mail]. Use [[ ]] with the =~ operator to check if email contains an @ symbol followed by characters and a dot. Print Valid email format if the regex matches.

Bash Scripting

lang="bash"
if [[ "$lang" == "bash" ]]; then
  echo "Match found"
fi
filename="report.txt"
if [[ "$filename" == *.txt ]]; then
  echo "Text file detected"
fi
# Set email and check with regex using =~
# Your code here

Need a hint?

Use [[ "$email" =~ @.+\..+ ]] — the regex must not be quoted.

4

Combining conditions with && and ||

Create two variables: age set to 25 and role set to admin. Use a single [[ ]] with && to check if age is greater than or equal to 18 AND role equals admin. Print Access granted if both conditions are true.

Bash Scripting

lang="bash"
if [[ "$lang" == "bash" ]]; then
  echo "Match found"
fi
filename="report.txt"
if [[ "$filename" == *.txt ]]; then
  echo "Text file detected"
fi
email="[e-mail]"
if [[ "$email" =~ @.+\..+ ]]; then
  echo "Valid email format"
fi
# Set age and role, check both conditions with && inside [[ ]]
# Your code here

Need a hint?

Use [[ $age -ge 18 && "$role" == "admin" ]] to combine conditions inside a single extended test.