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SPEC.md

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CNB Procfile format specification

This document outlines the format of a Procfile, which defines names to process types. For example:

web: rails s
worker: bundle exec sidekiq

Differences from Heroku "classic" Procfile

The classic Procfile has no formal specification. It is loosely defined based on a regex "^[[:space:]]*([a-zA-Z0-9_-]+):?\\s+(.*)[[:space:]]*. This specification is informed by the CNB specification for process names and kubernetes.

Specification

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

  • Spaces
    • The term spaces refers to non-newline whitespace characters such as tab '\t' or space '\s' characters.
  • Each line MUST contain a comment, empty line, or key/value pair.
  • Comments
    • A line MAY contain a comment
    • Comments MUST contain a # as the first visible character on each line.
    • A comment MAY be proceeded by one or more spaces.
  • Empty line
    • A Procfile MAY contain empty lines
    • An empty line MUST be zero or more spaces followed by a line ending or end of file (EOF).
  • Key/Value pairs
    • A line MAY contain a key/value pair where the key represents the name of a process and the value represents a command
    • A key MUST be separated from its value by a colon (:) followed by zero or more spaces.
    • Duplicate keys MUST be allowed and the last entry MUST take precedence. A warning SHOULD be issued.
  • Key
    • A key's first and last character MUST be a lowercase alphanumeric (a-z0-9) character (but not -).
    • All other key (middle) characters MUST be lowercase alphanumeric (a-z0-9) characters or hyphen -.
    • Key length MUST be within the range 1..=63
    • An implementation MAY accept _ as a middle character provided it converts it to - and issues a warning.
    • An implementation MAY accept an uppercase character provided it is converted to lowercase characters and issues a warning.
    • A key MAY be preceded with zero or more spaces provided they are not included in the return key and a warning is issued.
  • Value
    • A value MUST contain 1 or more non-whitespace characters.
    • A value MUST be terminated by a newline or EOF.