Pattern

Overview

A pattern describes the code to search for. The following string is an example of patterns for HCL which matches any aws_ebs_volume resource with any name and any configuration arguments:

resource "aws_ebs_volume" :[NAME] {
  :[...X]
}

Metavariable

In this example, :[NAME] behaves like a capture group in regular expressions; it matches one expression, identifier, or block, saving the matched part for use in code transformation. In general this notation is called metavariables.

Ellipsis Metavariable

:[...X] behaves almost same as :[X], but it matches zero or more expressions, identifiers, or blocks. This notation is called ellipsis metavariables.

Search with Metavariables

By using the same metavariable multiple times, you can search over your code, guaranteeing the equality of all the matched parts for the metavariable. For example, consider the following pattern:

attr1 = :[X]
attr2 = :[X]

This pattern DOES match (1) while it does NOT match (2):

// (1)
resource "hoge" "foo" {
  attr1 = 1
  attr2 = 1
}

// (2)
resource "hoge" "foo" {
  attr1 = 1
  attr2 = 2
}

📝 Tips: :[_] is called anonymous metavariable. The equality of the matched parts for :[_] will NOT be guaranteed; the following pattern matches both of (1) and (2).

attr1 = :[_]
attr2 = :[_]

Similarly, :[...] is called anonymous ellipsis metavariable, whose matched parts won't be tested for equivalence.