basic module system for bash
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README.md

README.md

Source As Module

Any bash library sourced with the help of source as module automatically has the library name prepended to the names of its functions. The sourced library does not need any knowledge of source as module, only your code does.

This is a way to namespace functions so that they do not conflict with your own. The effect is to emulate how other languages import functions from modules into their namespaces, languages such as Python and Ruby.

For the background on how source as module works, you can read my blog post.

Requirements

The sourced code must use the name() {} form of function declaration, not the function name {} form.

Installation

Clone this repository or download lib/as and put it somewhere in front of /usr/bin on your PATH.

Sourcing Regular Libraries with Source As Module

From your code:

source as module /path/to/foo.sh

or for multiple libraries:

source as module /path/to/foo.sh /path/to/bar.sh

/path/to is optional if foo.sh is on your PATH. That's a feature of source's normal behavior.

Let's say foo.sh defines the function foo. That function is now available to your code as foo.foo.

source as module drops the path and file extension from the filename to determine what name to use for the import. If you want to use a different name, use the following:

source as module bar=/path/to/foo.sh

This will import function foo as bar.foo. The same syntax works if you are sourcing multiple files.

foo (the unnamespaced version) is never instantiated, so your own foo definition won't be overwritten even if it exists before foo.sh is sourced.

Making Modules of Your Code

To make it so that your own library becomes a module when sourced by other files using the regular source command, add this at the top of your file:

source "$(dirname "$(readlink -f $BASH_SOURCE)")"/as module
module.already_loaded && return

Note that MacOS requires GNU readlink, called as greadlink, from homebrew.

In the shown use case, you'll want to distribute the as file with your script. However if as is on the PATH of the system already, you don't need the dirname and readlink calls, in which case the line is just source as module.

If your module is named bar.sh and defines a function named bar, that function will be available to any code which sources your module as bar.bar. The sourcing code doesn't need to know about source as module, it just sources your module with source /path/to/bar.sh.

This allows you to write and call your functions without namespacing them, but any file which sources your code will only see the namespaced versions. Calls to your functions from within your code will automatically be converted to use the namespaced versions as well.

source as module also defines a function called module.already_loaded which is used in the example above. It's only necessary when you are using source as module to make your own library be a module, but it is essential. You don't need it when you are loading regular (non-modular) libraries using source as module /path/to/foo.sh.

Other Notes

If your code creates any global variables then you may want to namespace those yourself manually by prefixing them with your module's name, e.g. foo_myvar. Global variables may otherwise conflict with the caller's. Unfortunately source as module can't help with namespacing of variables.

Note that source as module does leave some private functions and variables defined, but they are pre- and postfixed with an underscore so they aren't likely to cause conflict with yours.

Why Source As Module?

Why not just source module instead of source as module? Unfortunately, bash is a little weird when it comes to passing positional arguments to sourced files. You can pass arguments in the source call, but if you don't, then the caller's positional arguments are available instead. This gets confusing for source as module, since it uses the positional arguments to tell what it should do in the context of a particular invocation.

To always clear the caller's positional arguments, the alternatives are to either force you to call set -- before source as module or to require you to always feed the library a dummy argument. I've chosen the latter. To the reader's eye, I feel that source as module reads the most cleanly, so I've made the library's name as and require an argument of module.

Using Source As Module as a Library

To source just the functions defined by source as module's and not use its functionality, call source as library.