Common regex patterns in PowerShell - Mini Project: Build & Apply

Common regex patterns

📖 Scenario: You work in IT support and often need to check if user inputs match common patterns like email addresses, phone numbers, or postal codes.

🎯 Goal: Build a PowerShell script that uses common regex patterns to find matches in given text samples.

📋 What You'll Learn

Create variables with sample text strings

Define regex pattern variables for email, phone number, and postal code

Use the -match operator with the regex patterns to check for matches

Print the results clearly showing which pattern matched

💡 Why This Matters

🌍 Real World

IT support and automation scripts often need to validate user input like emails or phone numbers to ensure data quality.

💼 Career

Knowing common regex patterns and how to apply them in scripts is useful for system administrators, support engineers, and automation specialists.

1

Create sample text variables

Create three variables called $emailSample, $phoneSample, and $postalSample with these exact string values: '[e-mail]', '123-456-7890', and '90210' respectively.

PowerShell

# Your code here

Hint

Use = to assign the exact strings to the variables.

2

Define regex pattern variables

Create three variables called $emailPattern, $phonePattern, and $postalPattern with these exact regex strings: '^[\w.-]+@[\w.-]+\.[a-zA-Z]{2,}$' for email, '^\d{3}-\d{3}-\d{4}$' for phone number, and '^\d{5}$' for postal code.

PowerShell

$emailSample = '[e-mail]'
$phoneSample = '123-456-7890'
$postalSample = '90210'
# Your code here

Hint

Use single quotes and escape backslashes properly in regex strings.

3

Check matches using regex patterns

Use the -match operator with variables $emailSample, $phoneSample, and $postalSample against $emailPattern, $phonePattern, and $postalPattern respectively. Store the boolean results in variables $emailMatch, $phoneMatch, and $postalMatch.

PowerShell

$emailSample = '[e-mail]'
$phoneSample = '123-456-7890'
$postalSample = '90210'
$emailPattern = '^[\w.-]+@[\w.-]+\.[a-zA-Z]{2,}$'
$phonePattern = '^\d{3}-\d{3}-\d{4}$'
$postalPattern = '^\d{5}$'
# Your code here

Hint

Use -match to test if the sample matches the pattern and assign the result to the match variables.

4

Print the match results

Print the values of $emailMatch, $phoneMatch, and $postalMatch each on a new line using Write-Output.

PowerShell

$emailSample = '[e-mail]'
$phoneSample = '123-456-7890'
$postalSample = '90210'
$emailPattern = '^[\w.-]+@[\w.-]+\.[a-zA-Z]{2,}$'
$phonePattern = '^\d{3}-\d{3}-\d{4}$'
$postalPattern = '^\d{5}$'
$emailMatch = $emailSample -match $emailPattern
$phoneMatch = $phoneSample -match $phonePattern
$postalMatch = $postalSample -match $postalPattern
# Your code here

Hint

Use Write-Output to print each match result on its own line.

Practice

1. Which regex pattern matches any single digit from 0 to 9 in PowerShell?

easy

A. \d

B. \w

C. \s

D. \D

Solution

1. Step 1: Understand regex digit shorthand

   The pattern \d matches any single digit character (0-9) in regex.

2. Step 2: Compare other options

   \w matches word characters (letters, digits, underscore), \s matches whitespace, \D matches non-digit characters.

3. Final Answer:

   \d -> Option A

4. Quick Check:

   Digit shorthand = \d [OK]

Hint: Remember \d means digit, \w means word character [OK]

Common Mistakes:

• Confusing \d with \w or \s
• Using uppercase \D which means non-digit
• Thinking \w matches only letters

2. Which of the following is the correct PowerShell regex pattern to match a string that starts with 'abc'?

easy

A. abc*

B. abc$

C. ^abc

D. *abc

Solution

1. Step 1: Understand regex anchors

   The caret ^ matches the start of a string, so ^abc matches strings starting with 'abc'.

2. Step 2: Check other options

   abc$ matches strings ending with 'abc', abc* matches 'ab' followed by zero or more 'c's, *abc is invalid syntax.

3. Final Answer:

   ^abc -> Option C

4. Quick Check:

   Start anchor = ^abc [OK]

Hint: Use ^ at start to match beginning of string [OK]

Common Mistakes:

• Using $ instead of ^ for start of string
• Misunderstanding * as wildcard for any chars
• Placing * at start which is invalid

3. What will be the output of this PowerShell command?

$text = 'User123'
if ($text -match '\w{4}\d{3}') { 'Match' } else { 'No Match' }

medium

A. Match

B. No Match

C. Error

D. false

Solution

1. Step 1: Analyze the regex pattern

   \w{4} matches exactly 4 word characters, \d{3} matches exactly 3 digits. Together they match 7 characters: 4 word chars + 3 digits.

2. Step 2: Check the input string

   'User123' has 4 letters 'User' and 3 digits '123', so it matches the pattern.

3. Final Answer:

   Match -> Option A

4. Quick Check:

   4 letters + 3 digits = Match [OK]

Hint: Count characters to match {n} quantifiers exactly [OK]

Common Mistakes:

• Thinking \w includes only letters, ignoring digits
• Confusing {n} with * or + quantifiers
• Not escaping backslash properly in PowerShell string

4. Identify the error in this PowerShell regex usage:

$email = '[e-mail]'
if ($email -match '[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2}') { 'Valid' } else { 'Invalid' }

medium

A. Missing escape for dot before domain extension

B. Incorrect character class for username

C. Using single quotes prevents regex from working

D. Regex pattern is correct, no error

Solution

1. Step 1: Review regex pattern components

   The pattern matches username with allowed chars, an @, domain name, a literal dot (escaped), and domain extension of 2+ letters.

2. Step 2: Check PowerShell string usage

   Single quotes in PowerShell treat string literally, so \ is treated as a single backslash, correctly escaping the dot.

3. Final Answer:

   Regex pattern is correct, no error -> Option D

4. Quick Check:

   Proper escaping and pattern = Correct [OK]

Hint: Single quotes keep regex escapes intact in PowerShell [OK]

Common Mistakes:

• Thinking dot needs double escape in single quotes
• Assuming single quotes disable regex
• Misreading character classes as incorrect

5. You want to extract all words starting with a capital letter from a string in PowerShell. Which regex pattern should you use?

hard

A. \b[a-z][A-Z]*\b

B. \b[A-Z][a-z]*\b

C. [A-Z]+\b

D. \b[A-Z]+[0-9]*\b

Solution

1. Step 1: Understand the requirement

   We want words starting with a capital letter, followed by zero or more lowercase letters.

2. Step 2: Analyze each pattern

   A: \b[A-Z][a-z]*\b matches word boundary, one uppercase letter, then zero or more lowercase letters, then word boundary - correct.
   B: starts with lowercase letter, so incorrect.
   C: matches one or more uppercase letters but no word boundary start.
   D: matches uppercase letters followed by digits, not only letters.

3. Final Answer:

   \b[A-Z][a-z]*\b -> Option B

4. Quick Check:

   Capital start + lowercase letters = \b[A-Z][a-z]*\b [OK]

Hint: Use \b for word boundary and [A-Z] for capital start [OK]

Common Mistakes:

• Ignoring word boundaries causing partial matches
• Using [a-z][A-Z]* which starts with lowercase
• Including digits when only letters needed