PSRule/docs/expressions/functions.md

Functions

!!! Abstract Functions are an advanced language feature specific to YAML and JSON expressions. That extend the language to allow for more complex use cases with expressions. Functions don't apply to script expressions because PowerShell already has rich support for complex manipulation.

!!! Experimental Functions are a work in progress and subject to change. We hope to add more functions, broader support, and more detailed documentation in the future. Join or start a discussion to let us know how we can improve this feature going forward.

Functions cover two (2) main scenarios:

• Transformation — you need to perform minor transformation before a condition.
• Configuration — you want to configure an input into a condition.

Using functions

It may be necessary to perform minor transformation before evaluating a condition.

• boolean - Convert a value to a boolean.
• concat - Concatenate multiple values.
• configuration - Get a configuration value.
• first - Return the first element in an array or the first character of a string.
• integer - Convert a value to an integer.
• last - Return the last element in an array or the last character of a string.
• padLeft - Pad a value with a character on the left to meet the specified length.
• padRight - Pad a value with a character on the right to meet the specified length.
• path - Get a value from an object path.
• replace - Replace an old string with a new string.
• split - Split a string into an array by a delimiter.
• string - Convert a value to a string.
• substring - Extract a substring from a string.
• trim - Remove whitespace from the start and end of a string.

Supported conditions

Currently functions are only supported on a subset of conditions. The conditions that are supported are:

• equals
• notEquals
• count
• less
• lessOrEquals
• greater
• greaterOrEquals

Examples

---
# Synopsis: An expression function example.
apiVersion: github.com/microsoft/PSRule/v1
kind: Selector
metadata:
  name: Yaml.Fn.Example1
spec:
  if:
    value:
      $:
        substring:
          path: name
        length: 7
    equals: TestObj

---
# Synopsis: An expression function example.
apiVersion: github.com/microsoft/PSRule/v1
kind: Selector
metadata:
  name: Yaml.Fn.Example2
spec:
  if:
    value:
      $:
        configuration: 'ConfigArray'
    count: 5

---
# Synopsis: An expression function example.
apiVersion: github.com/microsoft/PSRule/v1
kind: Selector
metadata:
  name: Yaml.Fn.Example3
spec:
  if:
    value:
      $:
        boolean: true
    equals: true

---
# Synopsis: An expression function example.
apiVersion: github.com/microsoft/PSRule/v1
kind: Selector
metadata:
  name: Yaml.Fn.Example4
spec:
  if:
    value:
      $:
        concat:
        - path: name
        - string: '-'
        - path: name
    equals: TestObject1-TestObject1

---
# Synopsis: An expression function example.
apiVersion: github.com/microsoft/PSRule/v1
kind: Selector
metadata:
  name: Yaml.Fn.Example5
spec:
  if:
    value:
      $:
        integer: 6
    greater: 5

---
# Synopsis: An expression function example.
apiVersion: github.com/microsoft/PSRule/v1
kind: Selector
metadata:
  name: Yaml.Fn.Example6
spec:
  if:
    value: TestObject1-TestObject1
    equals:
      $:
        concat:
        - path: name
        - string: '-'
        - path: name

Recommended content

• Create a standalone rule
• Expressions
• Sub-selectors