Shell Imports

This is a handy utility for accessing a number of shell libraries across a number of scripts.

To use it just add the following line to any POSIX-compatible shell script:

if ! which shell_import_defined 2&>1 > /dev/null; then
	import_script=$(mktemp)
	curl -Ls -o "${import_script}" https://import.xurt.is/import.sh
	_="${import_script}"
	. "${import_script}"
	rm "${import_script}"
fi

Once that line is added any of the libraries provided by this repository can be added using the import command.

For example:

import color using span BOLD YELLOW_FG

echo "This is $(span $YELLOW_FG $BOLD "exciting")!"

You can also run command scripts from this repository with the run command.

Local install

You can maintain a local install of import by running the following in any terminal:

curl -Ls "https://import.xurt.is/local-import.sh" | sh

The command will print an alternative to add to scripts to use your local copy of install rather than the one loaded from the internet.

Adding that line to your init script should also override all uses of import to use your locally maintained version rather than fetching from the internet every time.

You can then update you install by either running the command run import-update with import already sourced as described above.

Writing scripts

This tool implements two concepts on top of the standard POSIX shell command language: scopes and namespaces (modules).

Writing functions with scopes

Writing functions with scopes is easy:

• Start every function with a scope statement, and
• Always use scope_return to leave a function.

foo () {
	scope

	if [ "$#" -gt 0 ]; then
		echo "Too many arguments" > /dev/stderr
		scope_return 1
	fi

	echo "This is foo"

	scope_return
}

Function scopes help to constrain local variables. Every variable should be declared using a var statement as in the following example.

factorial () {
	scope
	var factor = "$1"; shift

	case "$factor" in
		0)
			echo "1"
			;;
		*)
			var sub_factor = "$(factorial $((factor - 1)))"
			echo $((factor * sub_factor))
			;;
	esac
	scope_return
}

Constructing namespaced modules

A module is a collection of items including variables, constants, and functions.

To create a module, at the start of a script use the module statement and at the end use the end_module statement.

# Within foo.sh

module foo

# ... item declarations ...

pub fn bar
bar () {
	scope foo

	# ...

	scope_return
}

pub const BAZ = 1

pub const QUX = 2

end_module

To then use the public items from any of the modules declared in import libs, use an import statement.

# Imports bar and BAZ directly and QUZ as foo_QUX
import foo using bar BAZ

Any item can be made public by prefixing its declaration with pub.

Only public items can be used outside of the module.

All items from a module are implicitly imported with the prefix <name>_ where <name> was the argument of the module statement that was used to declare the module. This will usually be the same as the name of the script.

An import statement can be extended with a using statement followed by a list of item names to be imported without prefixing their names.

An alternative to import ... using ... is from ... use ... which will only import the explicitly named items keeping the scope less cluttered and faster to load.

Constants

The easiest items to create in a module are constants. An imported constant cannot be used to change its global value.

# Private constant, only visible within the module
const FOO = 1

# Public constant that cab be imported
pub const BAR = 2

Functions

Most items in modules will be functions. These are reusable sections of script that can be invoked as commands that use the same shell context.

Note: Some shell implementations such as zsh prevent the use of a (fairly sketchy) part of the POSIX shell standard that is required to implement the scoping of functions.

A function declaration in a module must be preceeded by a fn or pub fn statement as follows.

module qux

# Private function foo
fn foo
foo () {
	scope qux
	# ...
	scope_return
}

# Public function bar
pub fn bar
bar () {
	scope qux using foo
	# ...
	scope_return
}

# Public function baz, only uses foo from the module
pub fn baz
baz () {
	scope qux using foo
	# ...
	scope_return
}

end_module

Scope statements within functions should use the module name where they require any items provided by the module (including private items).

Where a function only requires a subset of the items from the module, the scope statement can be extended by adding using followed by the list of items required from the module. This may speed up functions from libraries with large numbers of items.

Variables

Modules can also export variables which will be updated globally.

module qux

# Private variable foo
var foo = 12

# Public variable bar
pub var bar = 12

end_module

When importing variables directly (i.e. with a using statement) any changes to the prefixed import will be ignored.

Libraries

• color