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Writing Expressions

Basic Syntax​

Expressions are written in CEL and look similar to expressions in C, JavaScript, or Python. They can include variables, literals, and operators.

Variables​

Variables are used to refer to values. For example, identity might refer to a user object.

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Supported Variables​

You can find the ngrok supported variables here:

Literals​

CEL supports several literal types:

  • Boolean: true, false
  • Integer: 42, -7
  • String: "hello", 'world'
  • List: [1, 2, 3]
  • Map: {"key1": "value1", "key2": "value2"}

Operators​

CEL provides a rich set of operators for performing arithmetic, comparison, and logical operations:

  • Arithmetic: +, -, *, /, %
  • Comparison: ==, !=, <, <=, >, >=
  • Logical: &&, ||, !

Using Arithmetic​

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Using Comparison and Logical Operators​

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Working with Strings​

String Concatenation​

To combine strings, use the + operator:

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String Functions​

CEL provides several built-in functions to work with strings, enabling you to perform transformations, query information, or compare strings.

size()​

Returns the number of characters in the string:

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startsWith()​

Checks if the string starts with a specified substring:

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endsWith()​

Checks if the string ends with a specified substring:

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matches()​

Determines if the string matches a regular expression pattern:

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contains()​

To check if a string contains another string:

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Advanced String Manipulation​

Regular Expressions​

CEL's matches() function allows you to use regular expressions for pattern matching. This can be powerful for validation or extracting parts of strings:

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Concatenation and Interpolation​

While direct string interpolation isn't a feature in CEL, concatenation can be used to dynamically construct strings:

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Working with Unicode​

Strings in CEL are Unicode and can handle a wide range of characters:

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String Comparison​

String comparison in CEL is case-sensitive and uses the standard comparison operators:

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Working with Lists​

A list in CEL is an ordered collection of elements. You can perform various operations on lists, including checking if an item is contained within a list, accessing elements by their index, and iterating over elements.

Creating a List​

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Checking for Membership​

To check if a value exists in a list, use the in operator:

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Accessing Elements​

Access elements by their index (0-based):

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Counting Elements​

Returns the number of elements in the list.

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Iterating Over a List​

Use a comprehension to iterate over elements in a list and apply logic:

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Filtering a List​

Filter a list to include only certain elements:

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Membership in Lists​

The in operator is versatile and can be used to check for membership in both lists:

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Working with Maps​

A map in CEL is a collection of key-value pairs. Keys are unique, and each key maps to exactly one value. You can check for the presence of keys, access values by their keys, and iterate over keys or values.

Creating a Map​

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Checking for Key Presence​

To check if a key is present in a map, use the in operator:

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Accessing Values​

Access values by their keys:

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Counting Elements​

Returns the number of key-value pairs present in the map.

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Iterating Over a Map​

You can iterate over the keys or values of a map using a comprehension:

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Checking for a Condition in a Map​

Use exists or all macros to check if any or all elements in a collection meet a condition:

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Membership in Maps​

The in operator is versatile and can be used to check for membership in maps:

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Conditional Expressions​

CEL supports ternary conditional expressions, allowing for simple if-then-else logic:

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Using Macros​

Macros provide syntactic sugar for common patterns, like looping through a collection:

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You can find the custom ngrok macros here: