---
sidebar_label: format
description: |-
  The format function produces a string by formatting a number of other values
  according to a specification string.
---

# `format` Function

The `format` function produces a string by formatting a number of other values according
to a specification string. It is similar to the `printf` function in C, and
other similar functions in other programming languages.

```hcl
format(spec, values...)
```

## Examples

```
> format("Hello, %s!", "Ander")
Hello, Ander!
> format("There are %d lights", 4)
There are 4 lights
```

Simple format verbs like `%s` and `%d` behave similarly to template
interpolation syntax, which is often more readable.

```
> format("Hello, %s!", var.name)
Hello, Valentina!
> "Hello, ${var.name}!"
Hello, Valentina!
```

The formatting verb `%#v` accepts a value of any type and presents it using JSON encoding, similar to jsonencode. This can be useful for describing the values given to a module in [custom condition check](../../language/expressions/custom-conditions.mdx#error-messages) error messages.

```
> format("%#v", "hello")
"\"hello\""
> format("%#v", true)
"true"
> format("%#v", 1)
"1"
> format("%#v", {a = 1})
"{\"a\":1}"
> format("%#v", [true])
"[true]"
> format("%#v", null)
"null"
```

The `format` function is most useful when you use more complex format specifications.

## Specification Syntax

The specification is a string that includes formatting verbs that are introduced
with the `%` character. The function call must then have one additional argument
for each verb sequence in the specification. The verbs are matched with
consecutive arguments and formatted as directed, as long as each given argument
is convertible to the type required by the format verb.

By default, `%` sequences consume successive arguments starting with the first.
Introducing a `[n]` sequence immediately before the verb letter, where `n` is a
decimal integer, explicitly chooses a particular value argument by its
one-based index. Subsequent calls without an explicit index will then proceed
with `n`+1, `n`+2, etc.

The function produces an error if the format string requests an impossible
conversion or access more arguments than are given. An error is produced also
for an unsupported format verb.

### Verbs

The specification may contain the following verbs.

| Verb  | Result                                                                                    |
| ----- | ----------------------------------------------------------------------------------------- |
| `%%`  | Literal percent sign, consuming no value.                                                 |
| `%v`  | Default formatting based on the [value type](#default-format-verbs). Accepts all types, including items of `null`, `list`, and `map` types.                           |
| `%#v` | JSON serialization of the value, as with `jsonencode`. Accepts all types, including items of `null`, `list`, and `map` types.  |
| `%t`  | Convert to boolean and produce `true` or `false`.                                         |
| `%b`  | Convert to integer number and produce binary representation.                              |
| `%d`  | Convert to integer number and produce decimal representation.                             |
| `%o`  | Convert to integer number and produce octal representation.                               |
| `%x`  | Convert to integer number and produce hexadecimal representation with lowercase letters.  |
| `%X`  | Like `%x`, but use uppercase letters.                                                     |
| `%e`  | Convert to number and produce scientific notation, like `-1.234456e+78`.                  |
| `%E`  | Like `%e`, but use an uppercase `E` to introduce the exponent.                            |
| `%f`  | Convert to number and produce decimal fraction notation with no exponent, like `123.456`. |
| `%g`  | Like `%e` for large exponents or like `%f` otherwise.                                     |
| `%G`  | Like `%E` for large exponents or like `%f` otherwise.                                     |
| `%s`  | Convert to string and insert the string's characters.                                     |
| `%q`  | Convert to string and produce a JSON quoted string representation.                        |

### Default Format Verbs

When `%v` is used, OpenTofu chooses the appropriate format verb based on the value type.

| Type      | Verb  |
| --------- | ----- |
| `string`  | `%s`  |
| `number`  | `%g`  |
| `bool`    | `%t`  |
| any other | `%#v` |

Null values produce the string `null` if formatted with `%v` or `%#v`, and cause an error for other verbs.

### Width Modifier

Use a width modifier with an optional decimal number immediately
preceding the verb letter to specify how many characters will be used to represent the value. You can specify precision after the (optional) width with a period (`.`) followed by a decimal number. If width or precision are omitted, OpenTofu selects default values based on the given value.

The following examples demonstrate example use cases for the width modifier.

| Sequence | Result                       |
| -------- | ---------------------------- |
| `%f`     | Default width and precision. |
| `%9f`    | Width 9, default precision.  |
| `%.2f`   | Default width, precision 2.  |
| `%9.2f`  | Width 9, precision 2.        |

:::note
Width and precision modifiers with non-numeric types such as
strings (`%s`) are interpreted differently. Setting either width or precision to
zero is the same as not including them at all.
:::

### Additional Format Options

Use the following symbols immediately after the `%` symbol to set additional formatting requirements.

| Symbol | Result                                                         |
| ------ | -------------------------------------------------------------- |
| space  | Leave a space where the sign would be if a number is positive. |
| `+`    | Show the sign of a number even if it is positive.              |
| `-`    | Pad the width with spaces on the right rather than the left.   |
| `0`    | Pad the width with leading zeros rather than spaces.           |


## Related Functions

* [`formatdate`](../../language/functions/formatdate.mdx) is a specialized formatting function for
  human-readable timestamps.
* [`formatlist`](../../language/functions/formatlist.mdx) uses the same specification syntax to
  produce a list of strings.
