zb-specific extensions

This section documents the functions that zb adds to its Lua environment. All the functions in this section are available as globals.

path{path[, name][, filter]}

Copies the file, directory, or symbolic link at p into the store. This is a common way of loading a program’s source code into zb.

When path is called from a Lua file inside the store directory, it cannot be called to access files outside the store directory.

Parameters:

  • path (string) – An absolute path or a path relative to the Lua file that called path. Slash-separated relative paths are accepted on all platforms.

  • name (string) – The name to use for the store object (excluding the digest). If omitted, then the last path component of path is used as the name.

  • filter (function) – If filter is given and path names a directory, then path calls filter for each file, directory, or symlink inside the directory. The first argument to the filter function is a slash-separated path relative to the top of the directory of the file currently being filtered. The second argument to the filter function is one of "regular", "directory", or "symlink" to indicate the type of the file. If the filter function returns nil or false, then the file will be excluded from import into the store. The default behavior of path is equivalent to passing filter = function() return true end.

Returns:

The absolute path to the imported store object.

Return type:

string

path(p)

As a convenience, if you only need to call path() with the path field, you can pass the string as the sole argument to path.

Parameters:

  • p (string) – An absolute path or a path relative to the Lua file that called path. Slash-separated relative paths are accepted on all platforms.

Returns:

The absolute path to the imported store object.

Return type:

string

readFile(p)

Added in version 0.2.

readFile reads the contents of a file into a string.

Parameters:

  • p (string) – An absolute path or a path relative to the Lua file that called readFile. Slash-separated relative paths are accepted on all platforms.

Returns:

The content of the file.

Return type:

string

derivation(env)

derivation adds a .drv file to the store specifying a derivation that can be built. derivation takes a table as its sole argument. All fields in the table are passed to the builder program as environment variables. The values can be strings, numbers, booleans, or lists of any of the previous types. A string is used as-is. Numbers are converted to strings. false is converted to the empty string; true is converted to the string 1. Each item in a list is converted to a string and then joined with a single space.

The returned derivation object will have a copy of all the fields of the table passed into the derivation function that produced it, plus a few extra fields:

  • drvPath: a string containing the absolute path to the resulting .drv file in the store.

  • out: a placeholder string that represents the absolute path to the derivation’s output. Passing this string (or strings formed from it) into other calls to derivation will implicitly add a build dependency between the derivations. (See “Dependency Information” for details.)

For convenience, using a derivation object in places that expect a string (e.g. concatenation or a call to tostring) will be treated the same as accessing the out field.

The environment that the builder runs in is documented in the Derivation Specification.

Parameters:

  • name (string) – The name to use for the derivation and the resulting store object (excluding the digest and the .drv extension).

  • system (string) – The triple that the derivation can run on.

  • builder (string) – The path to the program to run.

  • args (string[]) – The arguments to pass to the builder program.

  • outputHash (string) – If given, the derivation is a fixed-output derivation. This argument is a hash string for the derivation’s output, with its exact meaning determined by outputHashMode (see below). Derivations with the same name, outputHash, and outputHashMode are considered interchangable, regardless of the other fields in the derivation.

  • outputHashMode (string) – This field must not be set unless outputHash is also set. The value of the field must be one of flat (the default) or recursive. If the value of the field is flat or not set, then the builder must produce a single file and its contents, when hashed with the algorithm given by outputHash, must produce the same hash as outputHash. If the value of the field is recursive, then the builder’s output, when serialized as a NAR file and hashed with the algorithm given by outputHash, must produce the same hash as outputHash.

Return type:

derivation

fetchurl{url, hash[, name][, executable]}

fetchurl returns a derivation that downloads a URL. fetchurl takes a table as its sole argument with the following fields:

Parameters:

  • url (string) – The URL to download.

  • hash (string) – A hash string of the file’s content.

  • name (string) – The name to use for the store object (excluding the digest). If omitted, then the last path component of the url is used as the name.

  • executable (boolean) – Whether the file should be marked as executable. If true, then the NAR serialization is used to compute the hash instead of the file content.

Return type:

derivation

extract{src[, name][, stripFirstComponent]}

Returns a derivation that extracts an archive file.

The source must be in one of the following formats:

  • .tar

  • .tar.gz

  • .tar.bz2

  • .zip

The algorithm used to extract the archive is selected based on the first few bytes of the file.

Parameters:

  • src (string) – Path to the file.

  • name (string) – The name to use for the resulting store object (excluding the digest). If omitted, then the last path component of the src without the file extension is used as the name.

  • stripFirstComponent (boolean) – If true or omitted, then the root directory is stripped during extraction.

Return type:

derivation

fetchArchive{url, hash[, name][, stripFirstComponent]}

Returns a derivation that extracts an archive from a URL. This is a convenience wrapper around fetchurl and extract.

Parameters:

  • url (string) – The URL to download.

  • hash (string) – The hash string of the archive’s content (not the extracted store object).

  • name (string) – The name to use for the store object (excluding the digest). If omitted, then the last path component of the url is used as the name.

  • stripFirstComponent (boolean) – If true or omitted, then the root directory is stripped during extraction.

Return type:

derivation

import(path)

Reads the Lua file at the given path and executes it asynchronously. Every Lua file that zb encounters is treated as a separate module. This is similar to the dofile and require functions in standalone Lua (which are not supported in zb), but import is special in a few ways:

  • import will load the module for any given path at most once during a run of zb.

  • import does not execute the module right away. Instead, import returns a placeholder object that acts like the module. When you do anything with the placeholder object other than pass it around, it will then wait for the module to finish initialization. await can be used to access the value.

  • Globals are not shared among modules. Setting a “global” variable in a zb module will place it in a table which is implicitly returned by import if the module does not return any values.

  • Everything in a module will be “frozen” when the end of the file is reached. This means that any changes to variables or tables (even locals) will raise an error.

  • If path is a path constructed from a derivation, then zb will build the derivation before attempting to read it.

When import is called from a Lua file inside the store directory, it cannot be called to access files outside the store directory.

Parameters:

  • path (string) – An absolute path or a path relative to the Lua file that called path. Slash-separated relative paths are accepted on all platforms.

Returns:

A placeholder object for the module.

Return type:

module

await(x)

Forces a module (as returned by import) to load and returns its value. If the argument is not a module, then the argument is returned as-is.

toFile(name, s)

Creates a non-executable file in the store.

Parameters:

  • name (string) – File name (excluding digest)

  • s (string) – File content

Returns:

Absolute path to the store file

Return type:

string

storePath(path)

Adds a dependency on an existing store path. If the store object named by path does not exist in the store, storePath raises an error.

storePath is used to reference store objects that are created outside the zb build and imported into the store. Most users should avoid this function, as it is mostly intended for bootstrapping.

Parameters:
Returns:

A string that is equivalent to its argument but includes the dependency information necessary for it to be correctly interpreted as a store path. (See dependency information for details.)

Return type:

string

storeDir

storeDir is a string constant with the running evaluator’s store directory (e.g. /opt/zb/store or C:\zb\store).