Language

Introduction

This page describes the design and behavior of the language.

Preprocessing

Variables

Variables are alphabetic literals surrounded by %( and ). They are not interpreted. Instead they are replaced in the source using string substitution. For more information about variables see the Variables section of the reference.

Language

mktree uses a basic S-expression (“sexpr”) syntax to describe a tree of filesystem entities to create. The types are:

• Strings
• Numbers (unsigned integers)
• Attributes
• Filesystem entities

Strings

Strings are enclosed in double quotes. There are no supported escape sequences.

"This is a string."

Numbers

Numbers are parsed as unsigned integers. The bit-width is determined by the context when the number is evaluated. For example, when the number appears as @perm attribute on a directory or file, it is evaluated as an unsigned 32-bit integer and used as a file mode.

Attributes

Attributes begin with @ and are used to assign metadata to filesystem entities. Each entity supports different attributes. For example, the @contents attribute is used to set the contents of a file, but it’s invalid to set @contents on dir.

Filesystem entities

Filesystem entities such as directories and files are declared as sexprs. Each entity requires a name and may accept several attributes unique to the entity type. For more information about each kind of entity see the Filesystem entities section of the reference.

Comments

Comments begin with ‘;’ and span to the end of the current line. Comments may appear anywhere the source, including in the middle of sexprs.

; This is a comment

Grammar

tree      = stmt*
stmt      = comment
          | sexpr
comment   = ';' [^\n]*
sexpr     = '(' literal arg* ')'
arg       = sexpr
          | literal
literal   = KEYWORD
          | ATTRIBUTE
          | STRING
          | NUMBER
KEYWORD   = 'dir' | 'file' | 'link'
ATTRIBUTE = '@' [a-zA-Z0-9_-]+
STRING    = '"'[^"]*'"'
NUMBER    = [0-9]+