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just/GRAMMAR.md
Casey Rodarmor b6b01bf6d4 🔥 Disallow names that start with '-' (#154)
This is done for two reasons:

1. Such names cannot be given on the command line, since clap will
intercept them and wrongly interpret them as flags.

2. The name '---' can conflict with yaml document delimiters. Kind of
speculative, but I was thinking that it would be nice to make sure that
'---' and '...' are illegal in a justfile, so that that one can be
included in a yaml document stream. Is this silly? I am really not sure.

This is backwards incompatible, but I don't think anyone will notice,
since names that start with '-' are likely to be rare.
2017-02-10 20:15:25 -08:00

1.6 KiB

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 parameters.

tokens

BACKTICK            = `[^`\n\r]*`
COLON               = :
COMMENT             = #([^!].*)?$
NEWLINE             = \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

eol           : NEWLINE
              | COMMENT NEWLINE

assignment    : NAME '=' expression eol

export        : 'export' assignment

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

recipe        : '@'? NAME parameter* ('+' parameter)? ':' dependencies? body?

parameter     : NAME
              | NAME '=' STRING
              | NAME '=' RAW_STRING

dependencies  : NAME+

body          : INDENT line+ DEDENT

line          : LINE (TEXT | interpolation)+ NEWLINE
              | NEWLINE

interpolation : '{{' expression '}}'