9931f7f3c1
Adds the following edify functions: mount unmount format show_progress delete delete_recursive package_extract symlink set_perm set_perm_recursive This set is enough to extract and install the system part of a (full) OTA package. Adds the updater binary that extracts an edify script from the OTA package and then executes it. Minor changes to the edify core (adds a sleep() builtin for debugging, adds "." to the set of characters that can appear in an unquoted string).
109 lines
3.5 KiB
Plaintext
109 lines
3.5 KiB
Plaintext
Update scripts (from donut onwards) are written in a new little
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scripting language ("edify") that is superficially somewhat similar to
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the old one ("amend"). This is a brief overview of the new language.
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- The entire script is a single expression.
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- All expressions are string-valued.
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- String literals appear in double quotes. \n, \t, \", and \\ are
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understood, as are hexadecimal escapes like \x4a.
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- String literals consisting of only letters, numbers, colons,
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underscores, slashes, and periods don't need to be in double quotes.
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- The following words are reserved:
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if then else endif
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They have special meaning when unquoted. (In quotes, they are just
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string literals.)
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- When used as a boolean, the empty string is "false" and all other
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strings are "true".
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- All functions are actually macros (in the Lisp sense); the body of
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the function can control which (if any) of the arguments are
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evaluated. This means that functions can act as control
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structures.
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- Operators (like "&&" and "||") are just syntactic sugar for builtin
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functions, so they can act as control structures as well.
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- ";" is a binary operator; evaluating it just means to first evaluate
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the left side, then the right. It can also appear after any
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expression.
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- Comments start with "#" and run to the end of the line.
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Some examples:
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- There's no distinction between quoted and unquoted strings; the
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quotes are only needed if you want characters like whitespace to
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appear in the string. The following expressions all evaluate to the
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same string.
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"a b"
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a + " " + b
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"a" + " " + "b"
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"a\x20b"
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a + "\x20b"
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concat(a, " ", "b")
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"concat"(a, " ", "b")
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As shown in the last example, function names are just strings,
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too. They must be string *literals*, however. This is not legal:
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("con" + "cat")(a, " ", b) # syntax error!
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- The ifelse() builtin takes three arguments: it evaluates exactly
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one of the second and third, depending on whether the first one is
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true. There is also some syntactic sugar to make expressions that
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look like if/else statements:
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# these are all equivalent
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ifelse(something(), "yes", "no")
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if something() then yes else no endif
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if something() then "yes" else "no" endif
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The else part is optional.
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if something() then "yes" endif # if something() is false,
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# evaluates to false
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ifelse(condition(), "", abort()) # abort() only called if
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# condition() is false
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The last example is equivalent to:
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assert(condition())
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- The && and || operators can be used similarly; they evaluate their
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second argument only if it's needed to determine the truth of the
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expression. Their value is the value of the last-evaluated
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argument:
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file_exists("/data/system/bad") && delete("/data/system/bad")
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file_exists("/data/system/missing") || create("/data/system/missing")
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get_it() || "xxx" # returns value of get_it() if that value is
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# true, otherwise returns "xxx"
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- The purpose of ";" is to simulate imperative statements, of course,
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but the operator can be used anywhere. Its value is the value of
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its right side:
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concat(a;b;c, d, e;f) # evaluates to "cdf"
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A more useful example might be something like:
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ifelse(condition(),
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(first_step(); second_step();), # second ; is optional
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alternative_procedure())
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