String comparison (-like, -match) in PowerShell - Mini Project: Build & Apply

String Comparison with -like and -match in PowerShell

📖 Scenario: You are working with a list of file names in a folder. You want to find files that match certain patterns using PowerShell string comparison operators.

🎯 Goal: Learn how to use the -like and -match operators in PowerShell to filter strings based on patterns.

📋 What You'll Learn

Create a list of file names in a variable called files

Create a pattern variable called pattern for filtering

Use -like operator to filter files matching the pattern

Use -match operator to filter files matching a regex pattern

Print the filtered results

💡 Why This Matters

🌍 Real World

Filtering file names or text data based on patterns is common in automation scripts for organizing files or processing logs.

💼 Career

Knowing how to use string comparison operators like -like and -match in PowerShell helps automate tasks in system administration, DevOps, and scripting roles.

1

Create a list of file names

Create a variable called files and assign it an array with these exact file names: report1.txt, data.csv, summary.docx, report2.txt, image.png

PowerShell

# Create the array variable files with the given file names
# Your code here

Hint

Use @( ... ) to create an array in PowerShell.

2

Create a pattern variable for filtering

Create a variable called pattern and assign it the string 'report*.txt' to match files starting with 'report' and ending with '.txt' using wildcard.

PowerShell

$files = @('report1.txt', 'data.csv', 'summary.docx', 'report2.txt', 'image.png')
# Create the pattern variable with the value 'report*.txt'
# Your code here

Hint

Use single quotes for the string pattern with a wildcard *.

3

Filter files using -like operator

Use the -like operator to filter the files array for names matching the pattern. Store the result in a variable called likeMatches.

PowerShell

$files = @('report1.txt', 'data.csv', 'summary.docx', 'report2.txt', 'image.png')
$pattern = 'report*.txt'
# Filter files using -like and store in likeMatches
# Your code here

Hint

Use Where-Object { $_ -like $pattern } to filter the array.

4

Print the filtered results

Print the contents of the likeMatches variable using Write-Output.

PowerShell

$files = @('report1.txt', 'data.csv', 'summary.docx', 'report2.txt', 'image.png')
$pattern = 'report*.txt'
$likeMatches = $files | Where-Object { $_ -like $pattern }
# Print the likeMatches variable
# Your code here

Hint

Use Write-Output $likeMatches to display the filtered file names.

Practice

1. Which operator in PowerShell uses simple wildcard patterns for string comparison?

easy

A. -contains

B. -like

C. -match

D. -eq

Solution

1. Step 1: Understand the purpose of -like

   The -like operator uses simple wildcard characters like * and ? to match patterns in strings.

2. Step 2: Compare with -match

   The -match operator uses regular expressions, which are more complex than simple wildcards.

3. Final Answer:

   -like -> Option B

4. Quick Check:

   Simple wildcard matching = -like [OK]

Hint: Remember: -like = wildcards, -match = regex [OK]

Common Mistakes:

• Confusing -like with -match
• Thinking -contains works like -like
• Assuming -eq supports wildcards

2. Which of the following is the correct syntax to check if the variable $name contains the substring 'John' using -like?

easy

A. $name -like 'John*'

B. $name -like 'John?'

C. $name -like '*John*'

D. $name -like '?John?'

Solution

1. Step 1: Understand wildcard usage with -like

   The asterisk (*) wildcard matches zero or more characters. To check if 'John' appears anywhere, use '*John*'.

2. Step 2: Analyze each option

   $name -like 'John*' checks if string starts with 'John'. $name -like '*John*' checks if 'John' is anywhere. $name -like '?John?' uses '?' which matches exactly one character, so it won't match 'John' alone. $name -like 'John?' checks if string starts with 'John' and has one more character.

3. Final Answer:

   $name -like '*John*' -> Option C

4. Quick Check:

   Substring anywhere = '*John*' [OK]

Hint: Use * before and after substring to match anywhere [OK]

Common Mistakes:

• Forgetting to use * wildcards around substring
• Using ? instead of * for multiple characters
• Assuming -like matches exact substring without wildcards

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

$text = 'PowerShell123'
if ($text -match '\d{3}$') { 'Ends with 3 digits' } else { 'No match' }

medium

A. Ends with 3 digits

B. No match

C. Syntax error

D. Empty output

Solution

1. Step 1: Understand the regex pattern '\d{3}$'

   This pattern matches exactly three digits (\d{3}) at the end of the string ($).

2. Step 2: Check the string 'PowerShell123'

   The string ends with '123', which is three digits, so the pattern matches.

3. Final Answer:

   Ends with 3 digits -> Option A

4. Quick Check:

   Regex matches end digits = 'Ends with 3 digits' [OK]

Hint: Use -match with regex to find patterns like digits [OK]

Common Mistakes:

• Confusing -like with regex patterns
• Not escaping backslash in regex
• Assuming -match returns boolean instead of string output

4. Identify the error in this PowerShell snippet:

$file = 'report.doc'
if ($file -clike '*.DOC') { 'Match found' } else { 'No match' }

medium

A. -clike is case-sensitive, so '*.DOC' won't match 'report.doc'

B. Wildcard * is missing

C. Quotes around pattern are incorrect

D. Variable $file is not defined

Solution

1. Step 1: Understand the -clike operator

   -clike is the case-sensitive counterpart to -like. It requires exact case matching for the pattern.

2. Step 2: Analyze the mismatch

   The string 'report.doc' ends with lowercase '.doc', but the pattern '*.DOC' specifies uppercase '.DOC'. Other options are invalid: * is present, quotes are correct, $file is defined.

3. Final Answer:

   -clike is case-sensitive, so '*.DOC' won't match 'report.doc' -> Option A

4. Quick Check:

   Case mismatch with -clike = no match [OK]

Hint: Remember: -clike = case-sensitive, -like = case-insensitive [OK]

Common Mistakes:

• Forgetting -clike is case-sensitive
• Thinking wildcards are missing
• Misunderstanding variable initialization

5. You want to filter a list of filenames to include only those that start with 'log' and end with a 4-digit year using PowerShell. Which command correctly uses -match to do this?

$files = @('log2020.txt', 'log2019.csv', 'data2020.log', 'log20a0.txt')

hard

A. $files | Where-Object { $_ -like 'log????' }

B. $files | Where-Object { $_ -like 'log*2020' }

C. $files | Where-Object { $_ -match 'log\d{4}$' }

D. $files | Where-Object { $_ -match '^log\d{4}' }

Solution

1. Step 1: Understand the pattern requirements

   We want filenames starting with 'log' (^log) followed immediately by exactly 4 digits (\d{4}).

2. Step 2: Analyze each option

   $files | Where-Object { $_ -match '^log\d{4}' } uses regex '^log\d{4}' which matches strings starting with 'log' plus 4 digits. $files | Where-Object { $_ -like 'log????' } uses -like with 'log????' which matches 'log' plus any 4 characters but not necessarily digits. $files | Where-Object { $_ -match 'log\d{4}$' } matches 'log' followed by 4 digits at the end, but the year is not necessarily at the end of the filename. $files | Where-Object { $_ -like 'log*2020' } matches 'log' followed by anything and ending with '2020', which is too specific.

3. Final Answer:

   $files | Where-Object { $_ -match '^log\d{4}' } -> Option D

4. Quick Check:

   Start with 'log' + 4 digits = $files | Where-Object { $_ -match '^log\d{4}' } [OK]

Hint: Use ^ for start and \d{4} for 4 digits in regex [OK]

Common Mistakes:

• Using -like with ? instead of digits
• Matching digits at end instead of start
• Confusing -like and -match patterns