The Cloud Assembly blueprint expression syntax exposes all of the capabilities of expressions.

The syntax is only partly represented in the examples shown in How to use expressions to make Cloud Assembly blueprint code more versatile.

Literals

The following literals are supported:

  • Boolean (true or false)
  • Integer
  • Floating point
  • String

    Backslash escapes double quote, single quote, and backslash itself:

    " is escaped as \"

    ' is escaped as \'

    \ is escaped as \\

    Quotes only need to be escaped inside a string enclosed with the same type of quote, as shown in the following example.

    "I am a \"double quoted\" string inside \"double quotes\"."

  • Null

Environment variables

Environment names:

  • orgId
  • projectId
  • projectName
  • deploymentId
  • deploymentName
  • blueprintId
  • blueprintVersion
  • blueprintName
  • requestedBy (user)
  • requestedAt (time)

Syntax:

env.ENV_NAME

Example:

${env.blueprintId}

Resource variables

Resource variables let you bind to resource properties from other resources.

Syntax:

resource.RESOURCE_NAME.PROPERTY_NAME

Examples:

  • ${resource.db.id}
  • ${resource.db.networks[0].address}
  • ${resource.app.id} (Return the string for non-clustered resources, where count isn't specified. Return the array for clustered resources.)
  • ${resource.app[0].id} (Return the first entry for clustered resources.)

Resource self variables

Resource self variables are allowed only for resources supporting the allocation phase. Resource self variables are only available (or only have a value set) after the allocation phase is complete.

Syntax:

self.property_name

Example:

${self.address} (Return the address assigned during the allocation phase.)

Note that for a resource named resource_x, self.property_name and resource.resource_x.property_name are the same and are both considered self-references.

Cluster count index

Syntax:

count.index

Example:

${count.index == 0 ? "master" : "slave"} (Return the node type for clustered resources.)

Conditions

Syntax:

  • Equality operators are == and !=.
  • Relational operators are < > <= and >=.
  • Logical operators are && || and !.
  • Conditionals use the pattern:

    condition-expression ? true-expression : false-expression

Examples:

${input.count < 5 && input.size == 'small'}

${input.count < 2 ? "small" : "large"}

Arithmetic operators

Syntax:

Operators are + – / * and %.

Example:

${(input.count + 5) * 2}

String concatenation

Syntax:

${'ABC' + 'DEF'} evaluates to ABCDEF.

Operators [ ] and .

The expression follows ECMAScript in unifying the treatment of the [ ] and . operators.

So, expr.identifier is equivalent to expr["identifier"]. The identifier is used to construct a literal whose value is the identifier, and then the [ ] operator is used with that value.

Example:

${resource.app.networks[0].address}

In addition, when a property includes a space, delimit with square brackets and double quotes instead of using dot notation.

Incorrect:

input.operating system

Correct:

input["operating system"]

Construction of map

Syntax:

${{'key1':'value1', 'key2':input.key2}}

Construction of array

Syntax:

${['key1','key2']}

Example:

${[1,2,3]}

Functions

Syntax:

${function(arguments...)}

Example:

${to_lower(resource.app.name)}

Table 1. Functions
Function Description
abs(number) Absolute number value
floor(number) Returns the largest (closest to positive infinity) value that is less than or equal to the argument and is equal to a mathematical integer
ceil(number) Returns the smallest (closest to negative infinity) value that is greater than or equal to the argument and is equal to a mathematical integer
to_lower(str) Convert string to lower case
to_upper(str) Convert string to upper case
contains(array, value) Check if array contains a value
contains(string, value) Check if string contains a value
join(array, delim) Join array of strings with a delimiter and return a string
split(string, delim) Split string with a delimiter and return array of strings
slice(array, begin, end) Return slice of array from begin index to end index
reverse(array) Reverse entries of array
starts_with(subject, prefix) Check if subject string starts with prefix string
ends_with(subject, suffix) Check if subject string ends with suffix string
replace(string, target, replacement) Replace string containing target string with target string
substring(string, begin, end) Return substring of string from begin index until end index
format(format, values...) Return a formatted string using Java Class Formatter format and values.
keys(map) Return keys of map
values(map) Return values of map
merge(map, map) Return a merged map
length(string) Return string length
length(array) Return array length
max(array) Return maximum value from array of numbers
min(array) Return minimum value from array of numbers
sum(array) Return sum of all values from array of numbers
avg(array) Return average of all values from array of numbers
digest(value, type) Return digest of value using supported type (md5, sha1, sha256, sha384, sha512)
to_string(value) Return string representation of the value
to_number(string) Parse string as number
not_null(array) Return the first entry which is not null
base64_encode(string) Return base64 encoded value
base64_decode(string) Return decoded base64 value
now() Return current time in ISO-8601 format
uuid() Return randomly generated UUID
from_json(string) Parse json string
to_json(value) Serialize value as json string
json_path(value, path) Evaluate path against value using XPath for JSON.
matches(string, regex) Check if string matches a regex expression
url_encode(string) Encode string using url encoding specification
trim(string) Remove leading and trailing spaces