Regex match (~, ~*) in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Nginx regex match case sensitivity

Given the following nginx location block, what type of requests will it match?

location ~* ".*\.jpg$" { return 200; }

A Requests for URLs ending with .jpg or .JPG (case insensitive)

B Requests for URLs ending with .jpg only (case sensitive)

C Requests for URLs containing .jpg anywhere in the path (case sensitive)

D Requests for URLs ending with .JPG only (case sensitive)

💡 Hint

The ~* operator means case insensitive regex match.

The ~* operator in nginx means a case-insensitive regex match. The pattern ".*\.jpg$" matches any URL ending with .jpg or .JPG or any case variant.

💻 Command Output

intermediate

Nginx regex match case sensitivity difference

What is the difference in matching behavior between these two nginx location blocks?

location ~ ".*\.css$" { return 200; }
location ~* ".*\.css$" { return 200; }

A The first matches only .css exactly in lowercase; the second matches .css in any case

B Both match .css in any case

C The first matches .css in any case; the second matches only lowercase .css

D Both match only lowercase .css

💡 Hint

Check the difference between ~ and ~* operators.

The ~ operator is case sensitive regex match, so it matches only lowercase .css. The ~* operator is case insensitive, so it matches .css, .CSS, .Css, etc.

❓ Troubleshoot

advanced

Why does this nginx regex location not match uppercase extensions?

You have this nginx config:

location ~ ".*\.png$" { return 200; }

You notice requests for image.PNG return 404. Why?

A Because nginx does not support regex in location blocks

B Because the regex is invalid and nginx ignores it

C Because ~ is case sensitive and the regex only matches lowercase .png

D Because the $ anchor is misplaced causing no matches

💡 Hint

Consider the difference between ~ and ~* in nginx.

The ~ operator performs a case sensitive match. So .PNG does not match ".*\.png$". To match uppercase extensions, use ~*.

✅ Best Practice

advanced

Choosing regex match operator for nginx location

Which nginx location regex operator is best to match URLs ending with .html or .HTML regardless of case?

A Use prefix match with ".html"

B Use ~ operator with regex ".*\.html$"

C Use = operator with ".*\.html$"

D Use ~* operator with regex ".*\.html$"

💡 Hint

Think about case sensitivity and regex matching.

The ~* operator performs case-insensitive regex matching, so it matches .html and .HTML. The ~ operator is case sensitive. = is exact match, and prefix match does not support regex.

🧠 Conceptual

expert

Understanding nginx regex match precedence

Given these nginx location blocks:

location /images/ {
  return 404;
}
location ~* ".*\.jpg$" {
  return 200;
}

What happens when a request for /images/photo.JPG is made?

A The prefix location matches first and returns 404 because prefix locations have higher priority

B The regex location matches and returns 200 because regex locations have higher priority

C Nginx returns 404 because regex locations are ignored when prefix matches exist

D Nginx returns 200 because prefix locations are ignored when regex exists

💡 Hint

Nginx chooses regex locations over prefix if regex matches.

Nginx first finds the longest prefix match (/images/), then checks regex locations. If a regex location matches, it takes precedence over prefix. So /images/photo.JPG matches the regex location and returns 200.

Practice

1. What does the ~ operator mean in an nginx location block?

easy

A. It matches any request regardless of URL.

B. It performs a case-insensitive regular expression match.

C. It performs a case-sensitive regular expression match.

D. It matches the exact string only.

Solution

1. Step 1: Understand nginx regex operators

   The ~ operator in nginx is used for regex matching that is case-sensitive.

2. Step 2: Differentiate from ~*

   The ~* operator is for case-insensitive regex matching, so it is different from ~.

3. Final Answer:

   It performs a case-sensitive regular expression match. -> Option C

4. Quick Check:

   ~ = case-sensitive regex match [OK]

Hint: Remember: ~ is case-sensitive, ~* is case-insensitive [OK]

Common Mistakes:

• Confusing ~ with ~* for case sensitivity
• Thinking ~ matches exact strings only
• Assuming ~ matches all requests

2. Which of the following is the correct syntax to match URLs case-insensitively using regex in nginx?

easy

A. location ~* /images/ { }

B. location = /images/ { }

C. location ~ /images/ { }

D. location /images/ { }

Solution

1. Step 1: Identify case-insensitive regex syntax

   In nginx, ~* is used for case-insensitive regex matching.

2. Step 2: Check other options

   ~ is case-sensitive, = is exact match, and no operator means prefix match.

3. Final Answer:

   location ~* /images/ { } -> Option A

4. Quick Check:

   Case-insensitive regex = ~* [OK]

Hint: Use ~* for case-insensitive regex in nginx location [OK]

Common Mistakes:

• Using ~ instead of ~* for case-insensitive matching
• Confusing exact match (=) with regex
• Omitting regex operator for regex matching

3. Given this nginx config snippet:

location ~* \.jpg$ {
  return 200 'Image file matched';
}

What will be the response for a request to /photos/Sunset.JPG?

medium

A. 404 Not Found

B. 500 Internal Server Error

C. 200 with empty body

D. 200 with 'Image file matched'

Solution

1. Step 1: Analyze the regex and operator

   The ~* operator means case-insensitive regex match. The regex \.jpg$ matches strings ending with '.jpg' ignoring case.

2. Step 2: Check the request URL

   The request is /photos/Sunset.JPG, which ends with '.JPG' (uppercase). Case-insensitive match succeeds.

3. Final Answer:

   200 with 'Image file matched' -> Option D

4. Quick Check:

   Case-insensitive regex matches .JPG [OK]

Hint: ~* ignores case, so .JPG matches \.jpg$ regex [OK]

Common Mistakes:

• Assuming regex is case-sensitive with ~*
• Ignoring the $ end anchor in regex
• Confusing response codes returned

4. Identify the error in this nginx location block:

location ~* /images/(.*\.png$ {
  proxy_pass http://backend;
}

medium

A. Missing closing parenthesis in regex

B. Using ~* instead of ~ for case-sensitive match

C. proxy_pass URL is invalid

D. location block missing curly braces

Solution

1. Step 1: Check regex syntax

   The regex /images/(.*\.png$ has an opening parenthesis but no closing parenthesis.

2. Step 2: Validate other parts

   The ~* operator is valid for case-insensitive match, proxy_pass URL looks valid, and curly braces are present.

3. Final Answer:

   Missing closing parenthesis in regex -> Option A

4. Quick Check:

   Regex parentheses must be balanced [OK]

Hint: Count parentheses in regex to avoid syntax errors [OK]

Common Mistakes:

• Forgetting to close parentheses in regex
• Confusing ~ and ~* usage
• Ignoring syntax errors in regex patterns

5. You want to serve all URLs ending with .css or .CSS using a regex match in nginx. Which location block correctly matches both cases efficiently?

hard

A. location ~ \.css$ { }

B. location ~* \.css$ { }

C. location ~ \.css$|\.CSS$ { }

D. location ~* \.css$|\.CSS$ { }

Solution

1. Step 1: Understand case-insensitive matching

   Using ~* makes the regex case-insensitive, so it matches both '.css' and '.CSS'.

2. Step 2: Evaluate other options

   location ~ \.css$ { } uses case-sensitive ~, so it misses '.CSS'. Options C and D have incorrect regex syntax with unescaped pipes and redundant patterns.

3. Final Answer:

   location ~* \.css$ { } -> Option B

4. Quick Check:

   Use ~* for simple case-insensitive regex [OK]

Hint: Use ~* with simple regex to match case-insensitive extensions [OK]

Common Mistakes:

• Using ~ and missing uppercase matches
• Trying to match cases with complex regex instead of ~*
• Incorrect escaping of regex special characters