String functions (join, split, format) in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Terraform function join do?

The join function combines a list of strings into one string, using a specified separator between each element.

beginner

How does the split function work in Terraform?

The split function breaks a single string into a list of strings, using a specified separator to decide where to split.

beginner

Explain the purpose of the format function in Terraform.

The format function creates a formatted string by inserting values into placeholders inside a template string, similar to filling blanks in a sentence.

beginner

Example: What is the result of join(",", ["apple", "banana", "cherry"])?

The result is the string "apple,banana,cherry", which joins the list elements with commas.

beginner

Example: What does split(",", "red,green,blue") return?

It returns the list ["red", "green", "blue"] by splitting the string at each comma.

Which Terraform function would you use to combine a list of strings into one string?

A split

B join

C format

D concat

The join function combines list elements into a single string with a separator.

What does the split function return when given a string and a separator?

A A list of strings

B A number

C A single string

D A boolean

split breaks a string into a list of strings based on the separator.

How does the format function work in Terraform?

A It splits strings into lists

B It joins lists into strings

C It inserts values into a template string

D It converts strings to numbers

format creates a string by placing values into placeholders.

What is the output of join("-", ["a", "b", "c"])?

A "a,b,c"

B "abc"

C ["a", "b", "c"]

D "a-b-c"

The list elements are joined with dashes to form "a-b-c".

If you run split(":", "key:value"), what do you get?

A ["key", "value"]

B "key:value"

C "key"

D [":", "key", "value"]

The string is split at the colon into a list with two elements.

Describe how you would use Terraform string functions to convert a list of strings into a single comma-separated string.

Think about combining list items with a character between them.

Explain how the format function helps in creating dynamic strings in Terraform configurations.

Imagine writing a sentence where you fill in names or numbers dynamically.

Practice

1. What does the Terraform function join(",", ["a", "b", "c"]) return?

easy

A. "a,b,c"

B. ["a", "b", "c"]

C. "a b c"

D. "abc"

Solution

1. Step 1: Understand the join function

   The join function combines list elements into a single string using the given separator.

2. Step 2: Apply join with separator ','

   Joining ["a", "b", "c"] with "," results in the string "a,b,c".

3. Final Answer:

   "a,b,c" -> Option A

4. Quick Check:

   join with comma = "a,b,c" [OK]

Hint: Join combines list items with separator into one string [OK]

Common Mistakes:

• Confusing join output with original list
• Using space instead of comma as separator
• Expecting a list instead of a string

2. Which of the following is the correct syntax to split the string "one,two,three" into a list using Terraform?

easy

A. format(",", "one,two,three")

B. split("one,two,three", ",")

C. split(",", "one,two,three")

D. join(",", "one,two,three")

Solution

1. Step 1: Recall split function syntax

   The split function takes the separator first, then the string to split.

2. Step 2: Match correct argument order

   Only split(",", "one,two,three") matches the correct syntax.

3. Final Answer:

   split(",", "one,two,three") -> Option C

4. Quick Check:

   split(separator, string) = split(",", "one,two,three") [OK]

Hint: split(separator, string) order matters in Terraform [OK]

Common Mistakes:

• Swapping arguments order in split
• Using join instead of split
• Using format instead of split

3. What is the output of this Terraform expression?

format("Hello %s, you have %d messages", "Alice", 5)

medium

A. "Hello Alice, you have 5 messages"

B. "Hello Alice, you have %d messages"

C. "Hello %s, you have %d messages"

D. "Hello %s, you have 5 messages"

Solution

1. Step 1: Understand format placeholders

   %s is replaced by string, %d by integer in order.

2. Step 2: Replace placeholders with arguments

   "Alice" replaces %s, 5 replaces %d, producing "Hello Alice, you have 5 messages".

3. Final Answer:

   "Hello Alice, you have 5 messages" -> Option A

4. Quick Check:

   format with %s and %d = formatted string [OK]

Hint: format replaces %s and %d placeholders in order [OK]

Common Mistakes:

• Not replacing placeholders
• Mixing up %s and %d types
• Expecting original string without substitution

4. Identify the error in this Terraform code snippet:

locals {
  parts = split(",", "apple,banana,orange")
  result = join(";", parts)
  message = format("Fruits: %s", result)
}

medium

A. join separator should be a list, not a string

B. split function arguments are reversed

C. format placeholder %s cannot accept a string

D. No error, code is correct

Solution

1. Step 1: Check split function usage

   split separator and string are correctly ordered.

2. Step 2: Check join and format usage

   join uses string separator ";" correctly; format uses %s for string correctly.

3. Final Answer:

   No error, code is correct -> Option D

4. Quick Check:

   split, join, format used correctly = No error, code is correct [OK]

Hint: Check argument order and placeholder types carefully [OK]

Common Mistakes:

• Swapping split arguments
• Using wrong placeholder in format
• Passing wrong types to join

5. You have a list of IP addresses: ["10.0.0.1", "10.0.0.2", "10.0.0.3"]. You want to create a single string with these IPs separated by commas, but enclosed in square brackets like this:
[10.0.0.1,10.0.0.2,10.0.0.3]
Which Terraform expression achieves this?

hard

A. join(",", format("[%s]", ["10.0.0.1", "10.0.0.2", "10.0.0.3"]))

B. format("[%s]", join(",", ["10.0.0.1", "10.0.0.2", "10.0.0.3"]))

C. split(",", format("[%s]", join(",", ["10.0.0.1", "10.0.0.2", "10.0.0.3"])))

D. format(join(",", ["10.0.0.1", "10.0.0.2", "10.0.0.3"]), "[%s]")

Solution

1. Step 1: Join IP list with commas

   Using join(",", [...]) creates "10.0.0.1,10.0.0.2,10.0.0.3".

2. Step 2: Use format to add square brackets

   Wrapping the joined string with format("[%s]", ...) adds brackets around it.

3. Final Answer:

   format("[%s]", join(",", ["10.0.0.1", "10.0.0.2", "10.0.0.3"])) -> Option B

4. Quick Check:

   join then format = format("[%s]", join(",", ["10.0.0.1", "10.0.0.2", "10.0.0.3"])) [OK]

Hint: Join first, then format to add brackets [OK]

Common Mistakes:

• Trying to format before join
• Using split instead of join
• Incorrect argument order in format