github.com/Ilhicas/nomad@v1.0.4-0.20210304152020-e86851182bc3/website/content/docs/job-specification/hcl2/functions/encoding/csvdecode.mdx (about)

     1  ---
     2  layout: docs
     3  page_title: csvdecode - Functions - Configuration Language
     4  sidebar_title: csvdecode
     5  description: The csvdecode function decodes CSV data into a list of maps.
     6  ---
     7  
     8  # `csvdecode` Function
     9  
    10  `csvdecode` decodes a string containing CSV-formatted data and produces a
    11  list of maps representing that data.
    12  
    13  CSV is _Comma-separated Values_, an encoding format for tabular data. There
    14  are many variants of CSV, but this function implements the format defined
    15  in [RFC 4180](https://tools.ietf.org/html/rfc4180).
    16  
    17  The first line of the CSV data is interpreted as a "header" row: the values
    18  given are used as the keys in the resulting maps. Each subsequent line becomes
    19  a single map in the resulting list, matching the keys from the header row
    20  with the given values by index. All lines in the file must contain the same
    21  number of fields, or this function will produce an error.
    22  
    23  ## Examples
    24  
    25  ```shell-session
    26  > csvdecode("a,b,c\n1,2,3\n4,5,6")
    27  [
    28    {
    29      "a" = "1"
    30      "b" = "2"
    31      "c" = "3"
    32    },
    33    {
    34      "a" = "4"
    35      "b" = "5"
    36      "c" = "6"
    37    }
    38  ]
    39  ```
    40  
    41  <!---
    42  ## TODO: revamp this section
    43  
    44  ## Use with the `for_each` meta-argument
    45  
    46  You can use the result of `csvdecode` with
    47  [the `for_each` meta-argument](https://www.terraform.io/docs/configuration/resources.html#for_each-multiple-resource-instances-defined-by-a-map-or-set-of-strings)
    48  to describe a collection of similar objects whose differences are
    49  described by the rows in the given CSV file.
    50  
    51  There must be one column in the CSV file that can serve as a unique id for each
    52  row, which we can then use as the tracking key for the individual instances in
    53  the `for_each` expression. For example:
    54  
    55  ```hcl
    56  locals {
    57    # We've included this inline to create a complete example, but in practice
    58    # this is more likely to be loaded from a file using the "file" function.
    59    csv_data = <<-CSV
    60      local_id,instance_type,ami
    61      foo1,t2.micro,ami-54d2a63b
    62      foo2,t2.micro,ami-54d2a63b
    63      foo3,t2.micro,ami-54d2a63b
    64      bar1,m3.large,ami-54d2a63b
    65    CSV
    66  
    67    instances = csvdecode(local.csv_data)
    68  }
    69  
    70  resource "aws_instance" "example" {
    71    for_each = { for inst in local.instances : inst.local_id => inst }
    72  
    73    instance_type = each.value.instance_type
    74    ami           = each.value.ami
    75  }
    76  ```
    77  
    78  The `for` expression in our `for_each` argument transforms the list produced
    79  by `csvdecode` into a map using the `local_id` as a key, which tells
    80  Packer to use the `local_id` value to track each instance it creates.
    81  Packer will create and manage the following instance addresses:
    82  
    83  - `aws_instance.example["foo1"]`
    84  - `aws_instance.example["foo2"]`
    85  - `aws_instance.example["foo3"]`
    86  - `aws_instance.example["bar1"]`
    87  
    88  If you modify a row in the CSV on a subsequent plan, Packer will interpret
    89  that as an update to the existing object as long as the `local_id` value is
    90  unchanged. If you add or remove rows from the CSV then Packer will plan to
    91  create or destroy associated instances as appropriate.
    92  
    93  If there is no reasonable value you can use as a unique identifier in your CSV
    94  then you could instead use
    95  [the `count` meta-argument](https://www.terraform.io/docs/configuration/resources.html#count-multiple-resource-instances-by-count)
    96  to define an object for each CSV row, with each one identified by its index into
    97  the list returned by `csvdecode`. However, in that case any future updates to
    98  the CSV may be disruptive if they change the positions of particular objects in
    99  the list. We recommend using `for_each` with a unique id column to make
   100  behavior more predictable on future changes.
   101  -->