github.com/anth0d/nomad@v0.0.0-20221214183521-ae3a0a2cad06/website/content/docs/job-specification/hcl2/functions/string/format.mdx (about)

     1  ---
     2  layout: docs
     3  page_title: format - Functions - Configuration Language
     4  description: |-
     5    The format function produces a string by formatting a number of other values
     6    according to a specification string.
     7  ---
     8  
     9  # `format` Function
    10  
    11  `format` produces a string by formatting a number of other values according
    12  to a specification string. It is similar to the `printf` function in C, and
    13  other similar functions in other programming languages.
    14  
    15  ```hcl
    16  format(spec, values...)
    17  ```
    18  
    19  ## Examples
    20  
    21  ```shell-session
    22  > format("Hello, %s!", "Ander")
    23  Hello, Ander!
    24  > format("There are %d lights", 4)
    25  There are 4 lights
    26  ```
    27  
    28  Simple format verbs like `%s` and `%d` behave similarly to template
    29  interpolation syntax, which is often more readable:
    30  
    31  ```shell-session
    32  > format("Hello, %s!", var.name)
    33  Hello, Valentina!
    34  > "Hello, ${var.name}!"
    35  Hello, Valentina!
    36  ```
    37  
    38  The `format` function is therefore more useful when you use more complex format
    39  specifications, as described in the following section.
    40  
    41  ## Specification Syntax
    42  
    43  The specification is a string that includes formatting verbs that are introduced
    44  with the `%` character. The function call must then have one additional argument
    45  for each verb sequence in the specification. The verbs are matched with
    46  consecutive arguments and formatted as directed, as long as each given argument
    47  is convertible to the type required by the format verb.
    48  
    49  The specification may contain the following verbs:
    50  
    51  | Verb  | Result                                                                                    |
    52  | ----- | ----------------------------------------------------------------------------------------- |
    53  | `%%`  | Literal percent sign, consuming no value.                                                 |
    54  | `%v`  | Default formatting based on the value type, as described below.                           |
    55  | `%#v` | JSON serialization of the value, as with `jsonencode`.                                    |
    56  | `%t`  | Convert to boolean and produce `true` or `false`.                                         |
    57  | `%b`  | Convert to integer number and produce binary representation.                              |
    58  | `%d`  | Convert to integer number and produce decimal representation.                             |
    59  | `%o`  | Convert to integer number and produce octal representation.                               |
    60  | `%x`  | Convert to integer number and produce hexadecimal representation with lowercase letters.  |
    61  | `%X`  | Like `%x`, but use uppercase letters.                                                     |
    62  | `%e`  | Convert to number and produce scientific notation, like `-1.234456e+78`.                  |
    63  | `%E`  | Like `%e`, but use an uppercase `E` to introduce the exponent.                            |
    64  | `%f`  | Convert to number and produce decimal fraction notation with no exponent, like `123.456`. |
    65  | `%g`  | Like `%e` for large exponents or like `%f` otherwise.                                     |
    66  | `%G`  | Like `%E` for large exponents or like `%f` otherwise.                                     |
    67  | `%s`  | Convert to string and insert the string's characters.                                     |
    68  | `%q`  | Convert to string and produce a JSON quoted string representation.                        |
    69  
    70  When `%v` is used, one of the following format verbs is chosen based on the value type:
    71  
    72  | Type      | Verb  |
    73  | --------- | ----- |
    74  | `string`  | `%s`  |
    75  | `number`  | `%g`  |
    76  | `bool`    | `%t`  |
    77  | any other | `%#v` |
    78  
    79  Null values produce the string `null` if formatted with `%v` or `%#v`, and
    80  cause an error for other verbs.
    81  
    82  A width modifier can be included with an optional decimal number immediately
    83  preceding the verb letter, to specify how many characters will be used to
    84  represent the value. Precision can be specified after the (optional) width
    85  with a period (`.`) followed by a decimal number. If width or precision are
    86  omitted then default values are selected based on the given value. For example:
    87  
    88  | Sequence | Result                       |
    89  | -------- | ---------------------------- |
    90  | `%f`     | Default width and precision. |
    91  | `%9f`    | Width 9, default precision.  |
    92  | `%.2f`   | Default width, precision 2.  |
    93  | `%9.2f`  | Width 9, precision 2.        |
    94  
    95  The following additional symbols can be used immediately after the `%` symbol
    96  to set additoinal flags:
    97  
    98  | Symbol | Result                                                         |
    99  | ------ | -------------------------------------------------------------- |
   100  | space  | Leave a space where the sign would be if a number is positive. |
   101  | `+`    | Show the sign of a number even if it is positive.              |
   102  | `-`    | Pad the width with spaces on the left rather than the right.   |
   103  | `0`    | Pad the width with leading zeros rather than spaces.           |
   104  
   105  By default, `%` sequences consume successive arguments starting with the first.
   106  Introducing a `[n]` sequence immediately before the verb letter, where `n` is a
   107  decimal integer, explicitly chooses a particular value argument by its
   108  one-based index. Subsequent calls without an explicit index will then proceed
   109  with `n`+1, `n`+2, etc.
   110  
   111  The function produces an error if the format string requests an impossible
   112  conversion or access more arguments than are given. An error is produced also
   113  for an unsupported format verb.
   114  
   115  ## Related Functions
   116  
   117  - [`formatdate`](/docs/job-specification/hcl2/functions/datetime/formatdate) is a specialized formatting function for
   118    human-readable timestamps.
   119  - [`formatlist`](/docs/job-specification/hcl2/functions/string/formatlist) uses the same specification syntax to
   120    produce a list of strings.