Common regex patterns in PowerShell - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the regex pattern \d match?

It matches any single digit from 0 to 9.

beginner

What is the purpose of the regex pattern \w+?

It matches one or more word characters (letters, digits, or underscore).

beginner

Explain the regex pattern ^abc$.

It matches the exact string 'abc' only, from start (^) to end ($) of the line.

beginner

What does the regex pattern \s* match?

It matches zero or more whitespace characters (spaces, tabs, newlines).

beginner

How does the regex pattern [a-zA-Z] work?

It matches any single letter from a to z or A to Z (case sensitive).

Which regex pattern matches a string that starts with 'cat'?

A cat$

B cat*

C \bcat\b

D ^cat

The caret (^) means the start of the string, so '^cat' matches strings starting with 'cat'.

What does the regex pattern \D match?

A Any digit

B Any non-digit character

C Any whitespace

D Any word character

\D matches any character that is NOT a digit.

Which pattern matches one or more digits in a row?

A \d+

B \d*

C \d?

D \d{0}

\d+ matches one or more digits consecutively.

What does [0-9a-fA-F] match?

A Any digit or letter a-f or A-F

B Only digits 0-9

C Only letters a-f

D Only uppercase letters

It matches any hexadecimal digit: digits 0-9 and letters a-f or A-F.

Which regex matches zero or more whitespace characters?

A \s+

B \S*

C \s*

D \s?

\s* matches zero or more whitespace characters.

List and explain three common regex patterns used to match digits, words, and whitespace.

Think about shortcuts for digits, letters, and spaces.

Describe how anchors like ^ and $ are used in regex patterns.

Anchors fix where the pattern should appear in the text.

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