just/grammar.md

justfile grammar

Justfiles are processed by a mildly context-sensitive tokenizer and a recursive descent parser. The grammar is mostly LL(1), although an extra token of lookahead is used to distinguish between export assignments and recipes with arguments.

tokens

BACKTICK            = `[^`\n\r]*`
COLON               = :
COMMENT             = #([^!].*)?$
EOL                 = \n|\r\n
EQUALS              = =
INTERPOLATION_START = {{
INTERPOLATION_END   = }}
NAME                = [a-zA-Z_-][a-zA-Z0-9_-]*
PLUS                = +
RAW_STRING          = '[^'\r\n]*'
STRING              = "[^"]*" # also processes \n \r \t \" \\ escapes
INDENT              = emitted when indentation increases
DEDENT              = emitted when indentation decreases
LINE                = emitted before a recipe line
TEXT                = recipe text, only matches in a recipe body

grammar

justfile      : item* EOF

item          : recipe
              | assignment
              | export
              | EOL

assignment    : NAME '=' expression EOL

export        : 'export' assignment

expression    : STRING
              | RAW_STRING
              | NAME
              | expression '+' expression

recipe        : NAME arguments? ':' dependencies? body?

arguments     : NAME+

dependencies  : NAME+

body          : INDENT line+ DEDENT

line          : LINE (TEXT | interpolation)+ EOL

interpolation : '{{' expression '}}'