Switch with wildcard and regex in PowerShell

Introduction

The switch statement helps you check a value against many options easily. Using wildcards and regex lets you match patterns, not just exact words.

You want to run different code based on parts of a word or pattern.

You need to check if a filename matches certain patterns.

You want to handle user input that can vary but follows a pattern.

You want to simplify many <code>if</code> checks into one <code>switch</code>.

You want to find text that fits a pattern inside a list.

Syntax

PowerShell

switch -Wildcard ($value) {
  'pattern1' { # code }
  'pattern2' { # code }
}

switch -Regex ($value) {
  'regex1' { # code }
  'regex2' { # code }
}

-Wildcard lets you use * and ? to match parts of strings.

-Regex lets you use regular expressions for advanced pattern matching.

Examples

This checks if $word starts with 'cat', ends with 'dog', or contains 'bird'.

PowerShell

switch -Wildcard ($word) {
  'cat*' { "Starts with cat" }
  '*dog' { "Ends with dog" }
  '*bird*' { "Contains bird" }
}

This uses regex to do the same checks as above but with more power.

PowerShell

switch -Regex ($word) {
  '^cat' { "Starts with cat" }
  'dog$' { "Ends with dog" }
  'bird' { "Contains bird" }
}

Sample Program

This script checks the string 'catalog' with both wildcard and regex switches. The switch executes only the first matching case for each, printing the corresponding message.

PowerShell

$value = 'catalog'
switch -Wildcard ($value) {
  'cat*' { Write-Output "Matches wildcard: starts with 'cat'" }
  '*log' { Write-Output "Matches wildcard: ends with 'log'" }
  '*dog*' { Write-Output "Matches wildcard: contains 'dog'" }
  default { Write-Output "No wildcard match" }
}
switch -Regex ($value) {
  '^cat' { Write-Output "Matches regex: starts with 'cat'" }
  'log$' { Write-Output "Matches regex: ends with 'log'" }
  'dog' { Write-Output "Matches regex: contains 'dog'" }
  default { Write-Output "No regex match" }
}

Important Notes

Use default to catch values that don't match any pattern.

Wildcards are simpler but less powerful than regex.

Regex patterns can be tricky; test them carefully.

Summary

switch with -Wildcard matches simple patterns with * and ?.

switch with -Regex matches complex patterns using regular expressions.

Use these to write cleaner, easier-to-read code when checking many patterns.

Practice

1. What does the -Wildcard parameter do in a PowerShell switch statement?

easy

A. It matches patterns using complex regular expressions.

B. It makes the switch statement run faster by skipping checks.

C. It forces the switch to ignore case sensitivity.

D. It matches patterns using simple wildcards like * and ?.

Solution

1. Step 1: Understand the role of -Wildcard

   The -Wildcard parameter allows pattern matching using simple wildcards such as * (any characters) and ? (single character).

2. Step 2: Differentiate from -Regex

   Unlike -Regex, which uses complex regular expressions, -Wildcard is simpler and easier for basic pattern matching.

3. Final Answer:

   It matches patterns using simple wildcards like * and ?. -> Option D

4. Quick Check:

   -Wildcard = simple wildcard matching [OK]

Hint: Remember: Wildcard = * and ? patterns, Regex = complex patterns [OK]

Common Mistakes:

• Confusing -Wildcard with -Regex
• Thinking -Wildcard ignores case by default
• Assuming -Wildcard speeds up execution

2. Which of the following is the correct syntax to use a switch statement with wildcard matching in PowerShell?

easy

A. switch ($input) { '*test*' -Wildcard { 'Match' } }

B. switch ($input) -Wildcard { '*test*' { 'Match' } }

C. switch -Wildcard ($input) { '*test*' { 'Match' } }

D. switch ($input) { -Wildcard '*test*' { 'Match' } }

Solution

1. Step 1: Identify correct parameter placement

   In PowerShell, the -Wildcard parameter is placed immediately after switch and before the input expression.

2. Step 2: Check the pattern and block syntax

   The pattern '*test*' and the script block '{ 'Match' }' are correctly placed inside the switch braces.

3. Final Answer:

   switch -Wildcard ($input) { '*test*' { 'Match' } } -> Option C

4. Quick Check:

   Parameter right after switch keyword = switch -Wildcard ($input) { '*test*' { 'Match' } } [OK]

Hint: Put -Wildcard right after switch, before input [OK]

Common Mistakes:

• Placing -Wildcard inside the switch block
• Putting -Wildcard after the input variable
• Using -Wildcard as a pattern inside braces

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

switch -Regex ('apple', 'banana', 'cherry') {
  '^a' { 'Starts with a' }
  'an' { 'Contains an' }
  default { 'No match' }
}

medium

A. Starts with a
Contains an
No match

B. Starts with a
No match
No match

C. No match
Contains an
No match

D. Starts with a
Contains an
Contains an

Solution

1. Step 1: Check each input against regex patterns

   'apple' matches '^a' (starts with 'a'), so outputs 'Starts with a'. 'banana' contains 'an', so matches 'an' pattern, outputs 'Contains an'. 'cherry' matches none, so outputs 'No match'.

2. Step 2: Confirm output order

   The outputs correspond to each input in order: 'apple' -> 'Starts with a', 'banana' -> 'Contains an', 'cherry' -> 'No match'.

3. Final Answer:

   Starts with a Contains an No match -> Option A

4. Quick Check:

   Regex matches each input correctly = Starts with a Contains an No match [OK]

Hint: Match each input line by line with regex patterns [OK]

Common Mistakes:

• Assuming only first match per input
• Confusing regex anchors like ^
• Ignoring default case output

4. Identify the error in this PowerShell switch statement using wildcard matching:

switch ($word) -Wildcard {
  'he*' { 'Starts with he' }
  '*lo' { 'Ends with lo' }
  default { 'No match' }
}

medium

A. The -Wildcard parameter should be before the input variable.

B. The patterns 'he*' and '*lo' are invalid wildcards.

C. The default case is missing a script block.

D. The switch statement cannot use wildcards with variables.

Solution

1. Step 1: Check parameter placement

   The -Wildcard parameter must come immediately after the switch keyword, not after the input variable.

2. Step 2: Validate patterns and default block

   The patterns 'he*' and '*lo' are valid wildcards. The default case has a proper script block. Using wildcards with variables is allowed.

3. Final Answer:

   The -Wildcard parameter should be before the input variable. -> Option A

4. Quick Check:

   Parameter placement error = The -Wildcard parameter should be before the input variable. [OK]

Hint: Place -Wildcard right after switch, before input variable [OK]

Common Mistakes:

• Putting -Wildcard after input variable
• Thinking wildcards are invalid patterns
• Omitting script block braces

5. You want to categorize a list of filenames using switch with both wildcard and regex patterns. Which approach correctly combines -Wildcard and -Regex in one script to handle different patterns?

hard

A. Use a single switch with both -Wildcard and -Regex parameters together.

B. Use two separate switch statements: one with -Wildcard, one with -Regex, processing the list twice.

C. Use -Wildcard and -Regex as pattern modifiers inside one switch statement.

D. Use -Regex only and convert wildcards to regex patterns manually.

Solution

1. Step 1: Understand parameter exclusivity

   PowerShell's switch does not support using -Wildcard and -Regex together in one statement. They are mutually exclusive parameters.

2. Step 2: Choose practical approach

   To handle both wildcard and regex patterns, use two separate switch statements: one with -Wildcard and one with -Regex, processing the list twice.

3. Final Answer:

   Use two separate switch statements: one with -Wildcard, one with -Regex, processing the list twice. -> Option B

4. Quick Check:

   Separate switches for wildcard and regex = Use two separate switch statements: one with -Wildcard, one with -Regex, processing the list twice. [OK]

Hint: Use separate switches for wildcard and regex patterns [OK]

Common Mistakes:

• Trying to combine -Wildcard and -Regex in one switch
• Assuming pattern modifiers inside switch block
• Converting wildcards manually instead of separate switches