Regular expressions with -match in PowerShell - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the string contains the word 'cat'.

PowerShell

$text = 'The cat is sleeping.'
if ($text [1] 'cat') {
    Write-Output 'Found a cat!'
}

Drag options to blanks, or click blank then click option'

A-contains

B-match

C-like

D-eq

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-contains' which is for collections, not strings.

Using '-eq' which checks for exact equality.

The '-match' operator checks if the string matches the regular expression pattern.

2fill in blank

medium

Complete the code to check if the string starts with a digit using a regular expression.

PowerShell

$text = '3 cats'
if ($text [1] '^[0-9]') {
    Write-Output 'Starts with a digit'
}

Drag options to blanks, or click blank then click option'

A-like

B-eq

C-match

D-contains

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-like' which does not support full regex.

Using '-contains' which is for collections.

The '-match' operator supports regex patterns like '^[0-9]' to check the start of the string.

3fill in blank

hard

Fix the error in the code to check if the string ends with '.txt'.

PowerShell

$filename = 'document.txt'
if ($filename [1] '\.txt$') {
    Write-Output 'Text file detected'
}

Drag options to blanks, or click blank then click option'

A-like

B-eq

C-contains

D-match

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-like' which does not support regex anchors like '$'.

Using '-eq' which checks exact equality.

The '-match' operator is needed to use regex patterns like '\.txt$' to check the string ending.

4fill in blank

hard

Fill both blanks to create a regex that matches strings with exactly 3 digits.

PowerShell

$input = '123'
if ($input [1] '^[0-9][2]$') {
    Write-Output 'Exactly three digits'
}

Drag options to blanks, or click blank then click option'

A-match

B-like

C{3}

D{2}

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-like' which does not support regex quantifiers.

Using '{2}' which matches exactly two digits.

Use '-match' for regex matching and '{3}' to specify exactly three digits.

5fill in blank

hard

Fill all three blanks to create a regex that matches strings starting with 'a' or 'b' followed by one or more digits.

PowerShell

$text = 'a123'
if ($text [1] '^[[2]][0-9][3]$') {
    Write-Output 'Match found'
}

Drag options to blanks, or click blank then click option'

A-match

Bab

C+

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' which means zero or more, not one or more.

Using '-like' which does not support regex.

Use '-match' for regex, '[ab]' to match 'a' or 'b', and '+' to match one or more digits.

Practice

1. What does the -match operator do in PowerShell?

easy

A. Converts a string to uppercase

B. Replaces text in a string

C. Splits a string into an array

D. Checks if a string fits a pattern using regular expressions

Solution

1. Step 1: Understand the purpose of -match

   The -match operator is used to test if a string matches a regular expression pattern.

2. Step 2: Compare with other string operations

   Replacing text uses -replace, splitting uses -split, and uppercase conversion uses ToUpper(). These are different from -match.

3. Final Answer:

   Checks if a string fits a pattern using regular expressions -> Option D

4. Quick Check:

   -match = pattern check [OK]

Hint: Remember: -match means 'does it fit the pattern?' [OK]

Common Mistakes:

• Confusing -match with -replace or -split
• Thinking -match changes the string
• Assuming -match returns the matched text directly

2. Which of the following is the correct syntax to check if the variable $text contains the word 'hello' using -match?

easy

A. if ($text contains 'hello')

B. match $text 'hello'

C. $text -match 'hello'

D. $text =~ 'hello'

Solution

1. Step 1: Recall PowerShell -match syntax

   The correct syntax is $variable -match 'pattern' to test if the variable matches the pattern.

2. Step 2: Evaluate each option

   $text -match 'hello' uses the correct syntax. match $text 'hello' is invalid syntax. $text =~ 'hello' uses a Bash-like operator, not PowerShell. if ($text contains 'hello') uses a wrong operator for matching.

3. Final Answer:

   $text -match 'hello' -> Option C

4. Quick Check:

   Correct syntax = $text -match 'hello' [OK]

Hint: Use $var -match 'pattern' to test matches [OK]

Common Mistakes:

• Using Bash or other language operators like =~
• Writing match before the variable
• Using 'contains' instead of -match

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

$text = 'My phone number is 123-456-7890'
if ($text -match '\d{3}-\d{3}-\d{4}') {
  $matches[0]
} else {
  'No match'
}

medium

A. No match

B. 123-456-7890

C. \d{3}-\d{3}-\d{4}

D. My phone number is 123-456-7890

Solution

1. Step 1: Understand the regex pattern

   The pattern \d{3}-\d{3}-\d{4} matches a phone number format with three digits, a dash, three digits, a dash, and four digits.

2. Step 2: Check if the string matches and what $matches[0] contains

   The string contains '123-456-7890' which matches the pattern. $matches[0] holds the matched substring, so it outputs '123-456-7890'.

3. Final Answer:

   123-456-7890 -> Option B

4. Quick Check:

   Regex match found = matched text [OK]

Hint: Matched text is in $matches[0] after -match success [OK]

Common Mistakes:

• Expecting the whole string instead of matched part
• Confusing $matches with the pattern string
• Not escaping backslashes properly

4. Identify the error in this PowerShell snippet:

$text = 'Error code: 404'
if ($text -match '\d{3}') {
  Write-Output $matches
}

medium

A. You must use $matches[0] to get the matched string

B. The regex pattern is invalid

C. $matches is an automatic variable, no error here

D. You need to use -like instead of -match

Solution

1. Step 1: Understand $matches variable usage

   $matches is a hashtable holding matched groups. To get the matched string, you must access $matches[0].

2. Step 2: Analyze the code output

   Using Write-Output $matches prints the whole hashtable, not the matched string. To print the matched text, use Write-Output $matches[0].

3. Final Answer:

   You must use $matches[0] to get the matched string -> Option A

4. Quick Check:

   Print matched text with $matches[0] [OK]

Hint: Use $matches[0] to print matched text, not $matches alone [OK]

Common Mistakes:

• Printing $matches directly instead of $matches[0]
• Thinking $matches is a string, not a hashtable
• Confusing -match with -like operator

5. You want to extract all email addresses from a list of strings stored in $lines. Which PowerShell snippet correctly uses -match and $matches to collect emails into $emails?

hard

A. $emails = foreach ($line in $lines) { if ($line -match '[\w.-]+@[\w.-]+\.\w+') { $matches[0] } }

B. $emails = $lines -match '[\w.-]+@[\w.-]+\.\w+'

C. $emails = $lines | Where-Object { $_ -contains '[\w.-]+@[\w.-]+\.\w+' }

D. $emails = foreach ($line in $lines) { $line -match '[\w.-]+@[\w.-]+\.\w+' }

Solution

1. Step 1: Understand how to loop and match each line

   We must check each line with -match and if it matches, collect the matched email from $matches[0].

2. Step 2: Evaluate each option

   $emails = foreach ($line in $lines) { if ($line -match '[\w.-]+@[\w.-]+\.\w+') { $matches[0] } } loops through lines, tests with -match, and collects matched emails correctly. $emails = $lines -match '[\w.-]+@[\w.-]+\.\w+' tries to match the whole array at once, which doesn't work. $emails = $lines | Where-Object { $_ -contains '[\w.-]+@[\w.-]+\.\w+' } uses -contains which does not support regex. $emails = foreach ($line in $lines) { $line -match '[\w.-]+@[\w.-]+\.\w+' } runs -match but does not collect matched emails.

3. Final Answer:

   $emails = foreach ($line in $lines) { if ($line -match '[\w.-]+@[\w.-]+\.\w+') { $matches[0] } } -> Option A

4. Quick Check:

   Loop + -match + $matches[0] collects matches [OK]

Hint: Use foreach + if (-match) + $matches[0] to collect matches [OK]

Common Mistakes:

• Trying to match the whole array at once
• Using -contains instead of -match for regex
• Not collecting $matches[0] inside the loop