Common regex patterns in PowerShell - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this PowerShell regex match?

Given the string 'Contact: [e-mail]', what will be the output of this command?

$string = 'Contact: [e-mail]' if ($string -match '\b\w+@\w+\.\w+\b') { $matches[0] }

PowerShell

$string = 'Contact: [e-mail]'
if ($string -match '\b\w+@\w+\.\w+\b') { $matches[0] }

A [e-mail]

B Contact

C example.com

D No match

💡 Hint

Look for the pattern that matches an email format.

The regex matches a simple email pattern. The matched substring is '[e-mail]'.

💻 Command Output

intermediate

What does this regex extract from the date string?

Given the string 'Date: 2024-06-15', what will this command output?

$date = 'Date: 2024-06-15' if ($date -match '(\d{4})-(\d{2})-(\d{2})') { "$($matches[1])/$($matches[2])/$($matches[3])" }

PowerShell

$date = 'Date: 2024-06-15'
if ($date -match '(\d{4})-(\d{2})-(\d{2})') { "$($matches[1])/$($matches[2])/$($matches[3])" }

A No match

B Date

C 06-15-2024

D 2024/06/15

💡 Hint

The regex captures year, month, and day in groups.

The regex captures the year, month, and day parts separately and outputs them in YYYY/MM/DD format.

📝 Syntax

advanced

Which regex pattern matches a US phone number format?

Which option correctly matches a US phone number like [phone] in PowerShell regex?

A \d{3}-\d{3}-\d{4}

B \(\d{3}\) \d{3}-\d{4}

C \(\d{3}\)\d{3}-\d{4}

D \(\d{3}\) \d{3} \d{4}

💡 Hint

Look for the pattern with parentheses, space, and dash in correct places.

Option B matches the exact format with parentheses around area code, a space, then three digits, a dash, and four digits.

🔧 Debug

advanced

Why does this regex fail to match an IP address?

This PowerShell code tries to match an IP address but fails:

$ip = '192.168.1.1' if ($ip -match '\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}') { 'Match' } else { 'No match' }

Why does it fail?

A The dot (.) is not escaped, so it matches any character.

B The regex pattern is missing anchors ^ and $.

C The backslashes are not escaped properly in the regex string.

D The quantifiers {1,3} are invalid in PowerShell regex.

💡 Hint

Check how backslashes are handled in PowerShell strings.

In PowerShell, backslashes must be escaped in double-quoted strings or use single quotes. Here, the pattern uses single quotes but the backslash before dot is not doubled, so it is treated literally.

🚀 Application

expert

Extract all hashtags from a tweet using PowerShell regex

You have this tweet string:

$tweet = 'Learning #PowerShell and #regex is fun! #automation'

Which PowerShell command extracts all hashtags as an array?

A [regex]::Matches($tweet, '#\w+').ForEach({ $_.Value })

B [regex]::Matches($tweet, '#\w+').Value

C ([regex]::Matches($tweet, '#\w+')).Value

D [regex]::Matches($tweet, '#\w+').Cast().Select({ $_.Value })

💡 Hint

Look for a method to iterate over matches and extract their values.

Option A uses ForEach to iterate over the MatchCollection and extract the Value property of each match, returning an array of hashtags.

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