String Functions

String functions provide operations for text manipulation, formatting, and pattern matching in HCL expressions.

Function Reference

chomp

Removes newline characters at the end of a string.

chomp(string)

Parameters:

• string - The string to process

Returns: String with trailing newlines removed

Example:

chomp("hello world\n")      # Returns: "hello world"
chomp("hello\n\n")          # Returns: "hello"
chomp("hello")              # Returns: "hello"

format

Produces a string by formatting values according to a specification string.

format(spec, values...)

Parameters:

• spec - Format specification string
• values... - Values to format

Returns: Formatted string

Format Verbs:

• %s - String
• %d - Integer
• %f - Float
• %t - Boolean
• %% - Literal percent sign

Example:

format("Hello %s", "world")           # Returns: "Hello world"
format("Port %d", 8080)               # Returns: "Port 8080"
format("%s-%02d", "web", 1)           # Returns: "web-01"
format("%.2f%%", 99.9)                # Returns: "99.90%"

formatlist

Produces a list of strings by formatting according to a specification string.

formatlist(spec, values...)

Parameters:

• spec - Format specification string
• values... - Lists of values to format

Returns: List of formatted strings

Example:

formatlist("hello %s", ["alice", "bob", "charlie"])
# Returns: ["hello alice", "hello bob", "hello charlie"]

formatlist("%s-%d", ["web", "api"], [1, 2])
# Returns: ["web-1", "api-2"]

indent

Adds spaces to the beginning of each line in a multi-line string.

indent(spaces, string)

Parameters:

• spaces - Number of spaces to add
• string - String to indent

Returns: Indented string

Example:

indent(2, "line1\nline2\nline3")
# Returns: "line1\n  line2\n  line3"

# Useful for formatting YAML in templates
indent(4, jsonencode({key = "value"}))

join

Concatenates list elements into a single string with a separator.

join(separator, list)

Parameters:

• separator - String to place between elements
• list - List of strings to join

Returns: Joined string

Example:

join(", ", ["apple", "banana", "cherry"])    # Returns: "apple, banana, cherry"
join("-", ["2024", "01", "15"])               # Returns: "2024-01-15"
join("", ["h", "e", "l", "l", "o"])          # Returns: "hello"

lower

Converts all cased letters to lowercase.

lower(string)

Parameters:

• string - String to convert

Returns: Lowercase string

Example:

lower("HELLO WORLD")        # Returns: "hello world"
lower("MixedCase")          # Returns: "mixedcase"
lower("already lower")      # Returns: "already lower"

regex

Applies a regular expression and returns the first match.

regex(pattern, string)

Parameters:

• pattern - Regular expression pattern
• string - String to search

Returns: First matching substring or error if no match

Example:

regex("[0-9]+", "abc123def")              # Returns: "123"
regex("^[a-z]+", "hello123")              # Returns: "hello"
regex("v([0-9.]+)", "version: v1.2.3")    # Returns: "1.2.3"

regexall

Applies a regular expression and returns all matches.

regexall(pattern, string)

Parameters:

• pattern - Regular expression pattern
• string - String to search

Returns: List of all matching substrings

Example:

regexall("[0-9]+", "abc123def456")     # Returns: ["123", "456"]
regexall("[a-z]+", "hello123world")    # Returns: ["hello", "world"]
regexall(".", "abc")                   # Returns: ["a", "b", "c"]

split

Divides a string into a list at separator occurrences.

split(separator, string)

Parameters:

• separator - String to split on
• string - String to split

Returns: List of string parts

Example:

split(",", "apple,banana,cherry")     # Returns: ["apple", "banana", "cherry"]
split(".", "192.168.1.1")             # Returns: ["192", "168", "1", "1"]
split(" ", "hello world")             # Returns: ["hello", "world"]

strrev

Reverses the characters in a string.

strrev(string)

Parameters:

• string - String to reverse

Returns: Reversed string

Example:

strrev("hello")           # Returns: "olleh"
strrev("12345")           # Returns: "54321"
strrev("racecar")         # Returns: "racecar"

substr

Extracts a substring by position and length.

substr(string, offset, length)

Parameters:

• string - String to extract from
• offset - Starting position (0-based)
• length - Maximum characters to extract

Returns: Extracted substring

Example:

substr("hello world", 0, 5)     # Returns: "hello"
substr("hello world", 6, 5)     # Returns: "world"
substr("hello world", 6, 100)   # Returns: "world" (length exceeds string)

title

Capitalizes the first letter of each word.

title(string)

Parameters:

• string - String to convert

Returns: Title-cased string

Example:

title("hello world")              # Returns: "Hello World"
title("the quick brown fox")      # Returns: "The Quick Brown Fox"
title("API_KEY")                  # Returns: "Api_key"

trim

Removes whitespace from both ends of a string (custom hclconfig implementation).

trim(string)

Parameters:

• string - String to trim

Returns: Trimmed string

Example:

trim("   hello   ")          # Returns: "hello"
trim("\n\thello\n\t")        # Returns: "hello"
trim("hello")                # Returns: "hello"

trimprefix

Removes a prefix from the start of a string.

trimprefix(string, prefix)

Parameters:

• string - String to process
• prefix - Prefix to remove

Returns: String with prefix removed (only if present)

Example:

trimprefix("helloworld", "hello")     # Returns: "world"
trimprefix("helloworld", "world")     # Returns: "helloworld"
trimprefix("/path/to/file", "/")      # Returns: "path/to/file"

trimsuffix

Removes a suffix from the end of a string.

trimsuffix(string, suffix)

Parameters:

• string - String to process
• suffix - Suffix to remove

Returns: String with suffix removed (only if present)

Example:

trimsuffix("helloworld", "world")     # Returns: "hello"
trimsuffix("helloworld", "hello")     # Returns: "helloworld"
trimsuffix("file.txt", ".txt")        # Returns: "file"

trimspace

Removes whitespace from both ends of a string.

trimspace(string)

Parameters:

• string - String to trim

Returns: String with whitespace removed

Example:

trimspace("  hello  ")           # Returns: "hello"
trimspace("\n\thello\n\t")       # Returns: "hello"
trimspace("hello")               # Returns: "hello"

upper

Converts all cased letters to uppercase.

upper(string)

Parameters:

• string - String to convert

Returns: Uppercase string

Example:

upper("hello world")        # Returns: "HELLO WORLD"
upper("MixedCase")          # Returns: "MIXEDCASE"
upper("ALREADY UPPER")      # Returns: "ALREADY UPPER"

Common Use Cases

Normalizing User Input

local {
  # Clean and normalize username
  username = lower(trimspace(var.raw_username))

  # Remove file extension
  name_without_ext = trimsuffix(var.filename, ".txt")
}

Building Dynamic Names

resource "container" "web" {
  count = 3

  container_name = format("%s-web-%02d", var.environment, count.index + 1)
  # Results: "prod-web-01", "prod-web-02", "prod-web-03"
}

Parsing Configuration

local {
  # Split comma-separated values
  allowed_ips = split(",", var.ip_whitelist)

  # Extract parts using regex
  version_number = regex("v([0-9.]+)", var.image_tag)
}

Template Processing

resource "template" "config" {
  source = format(<<-EOF
    server {
      listen %d;
      server_name %s;
      root %s;
    }
  EOF
  , var.port, lower(var.domain), trimprefix(var.path, "/"))

  destination = "./nginx.conf"
}