Named captures in PowerShell - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of Named Capture Groups in PowerShell Regex

What is the output of this PowerShell script using named capture groups?

PowerShell

$text = 'User: Alice, Age: 30'
if ($text -match '(?<name>User: \w+), Age: (?<age>\d+)') {
  "$($matches['name']) and $($matches['age'])"
} else {
  'No match'
}

A User: Alice and 30

B Alice and 30

C No match

D User: Alice, Age: 30

💡 Hint

Remember that named captures include the full matched text for the group name.

The named capture 'name' captures 'User: Alice' including the label, and 'age' captures '30'. The script outputs both exactly as captured.

💻 Command Output

intermediate

Extracting Named Groups with Multiple Matches

What will be the output of this PowerShell script that uses named captures with multiple matches?

PowerShell

$text = 'ID:123 Name:John; ID:456 Name:Jane'
$pattern = '(ID:(?<id>\d+)) Name:(?<name>\w+)'
$matches = [regex]::Matches($text, $pattern)
foreach ($m in $matches) {
  "$($m.Groups['id'].Value) - $($m.Groups['name'].Value)"
}

A No output

B

ID:123 - Name:John
ID:456 - Name:Jane

C

123 Name:John
456 Name:Jane

D

123 - John
456 - Jane

💡 Hint

Look at how the named groups 'id' and 'name' are accessed from each match.

The regex matches two groups: 'id' captures digits after 'ID:', and 'name' captures the word after 'Name:'. The foreach loop prints each pair separated by ' - '.

🔧 Debug

advanced

Identify the Error in Named Capture Usage

What error will this PowerShell script produce when run?

PowerShell

$text = 'Error 404: Not Found'
if ($text -match '(?<code>\d+): (?<message>.+)') {
  Write-Output $matches['code']
  Write-Output $matches['message']
} else {
  Write-Output 'No match'
}

A No match

B

404
Not Found

C Runtime error: Index operation failed

D Syntax error

💡 Hint

Check if the regex pattern matches the input string exactly.

The regex expects a colon ':' immediately after digits, but the input has 'Error 404: Not Found' with a space before digits. The match fails, so 'No match' is output.

🧠 Conceptual

advanced

Understanding Named Capture Group Behavior

In PowerShell, what does the named capture group store in the automatic $matches variable after a successful regex match?

A The entire input string matched by the regex

B Only the text matched inside the parentheses of the named group

C The index position of the match in the input string

D The name of the group as a string

💡 Hint

Think about what a capture group is designed to extract.

Named capture groups store the substring matched inside their parentheses, accessible by the group name in $matches.

🚀 Application

expert

Extracting and Using Named Captures in a Script

Given the text 'Order #12345: Product=Book, Qty=3', which PowerShell script correctly extracts the order number, product name, and quantity using named captures and outputs them as JSON?

A

$text = 'Order #12345: Product=Book, Qty=3'
if ($text -match 'Order #(?<order>\d+): Product=(?<product>\w+), Qty=(?<qty>\d+)') {
  $obj = [PSCustomObject]@{
    OrderNumber = $matches.order
    ProductName = $matches.product
    Quantity = $matches.qty
  }
  $obj | ConvertTo-Json
}

B

$text = 'Order #12345: Product=Book, Qty=3'
if ($text -match 'Order #(?<order>\d+): Product=(?<product>\w+), Qty=(?<qty>\d+)') {
  $obj = [PSCustomObject]@{
    OrderNumber = $matches['order']
    ProductName = $matches['product']
    Quantity = [int]$matches['qty']
  }
  $obj | ConvertTo-Json
}

C

$text = 'Order #12345: Product=Book, Qty=3'
if ($text -match 'Order #(?<order>\d+): Product=(?<product>\w+), Qty=(?<qty>\d+)') {
  $obj = [PSCustomObject]@{
    OrderNumber = $matches['order']
    ProductName = $matches['product']
    Quantity = $matches['qty']
  }
  $obj | ConvertTo-Json
}

D

$text = 'Order #12345: Product=Book, Qty=3'
if ($text -match 'Order #(?<order>\d+): Product=(?<product>\w+), Qty=(?<qty>\d+)') {
  $obj = @{OrderNumber=$matches.order; ProductName=$matches.product; Quantity=$matches.qty}
  $obj | ConvertTo-Json
}

💡 Hint

Access named captures from $matches using the correct syntax and convert quantity to integer if needed.

Option C correctly accesses named captures using $matches['name'] syntax and creates a PSCustomObject, then converts it to JSON. It matches PowerShell syntax and best practice.