Oobash

An object-oriented programming library for bash. Sourcing oobash.sh allows you to define objects in bash scripts which have properties, methods, and inheritance. They're less like Java classes and more like Lua tables, in that there's no class/object distinction; each object just has a parent, to which it will look for methods and properties not defined on it.

Oobash currently has no external dependencies (not even on standard utilities), although it does use features of bash 4 and will not work in earlier versions. It also keeps its metadata entirely in environment variables, not the filesystem. I reserve the right to change either of those constraints in the future if it facilitates implementing something cool, but I prefer not to as long as other options are available.

Getting Help & Contributing

Feel free to open issues in this repository, or make pull requests with small changes. If you would like to make a large change, please open an issue first to propose it.

Usage Cheatsheet

eval $(new object my_obj)
my_obj property = 'value'
my_obj property
# prints: value

my_obj method << 'EOF'
  # arguments: $1, $2 ...
  # this object: $self
  # parent object: $super
  echo hi
EOF

my_obj method
# prints: hi

eval $(new object other_obj)
other_obj property = $(my_obj property)
other_obj property
# prints: value

Example Walkthrough

The example dissected below is test.sh in this repo.

Fetch a local copy of oobash.

curl -O https://raw.githubusercontent.com/relsqui/oobash/master/oobash.sh

Source it in your script. This will add functions called new and object to your environment, as well as a number of functions and variables with the prefix oob_.

source oobash.sh

Create new objects by calling new followed by the names of the parent object and the new object, in that order, and evaluating the result. Every object must have a parent; use the base object when you don't need another one. This creates an object called widget:

eval $(new object widget)

Set properties on an object with the syntax object_name property_name = value. Values are parsed like bash arguments and stored like bash variables, so put them in quotes if they contain spaces, escape special characters, and so on.

widget name = 'Widget Class'

Define methods with herestring syntax. The __constructor method is special, and will be run every time you create an object as a child of the one you defined the constructor on.

This constructor assigns every widget we create a number, incrementing each time:

widget_count=0

widget __constructor << 'EOF'
    let widget_count++
    $self widget_number = $widget_count
EOF

Note that you also have $self available to refer to an object from inside its own methods.

Like other bash functions, oobash methods can access their arguments with $1, $2, and so on. They can also use $super to refer to the object defined as their parent.

To retrieve the value of an oobash object property inline, enclose it in $() (or backticks) -- you're actually running a function which outputs the value.

widget introduce << 'EOF'
    echo "Hi, I'm $($self name), widget #$($self widget_number)."
    echo "My parent is $($super name)."
    echo "Please meet my friend, $($1 name)."
EOF

Having defined an object with some methods, you can instantiate child objects and give them different properties (as well as additional methods).

eval $(new widget widget1)
widget1 name = 'Widgeter'

eval $(new widget widget2)
widget2 name = 'Widgetest'

Child objects can call methods defined on their parent.

$ widget2 introduce widget1
Hi, I'm Widgetest, widget #2.
My parent is Widget Class.
Please meet my friend, Widgeter.

To see what's happening under the hood (such as when debugging inheritance problems), you can export the environment variable OOB_DEBUG with any non-empty value.

----[widget1] introduce widget2
----searching widget1's parent for introduce
------[widget] introduce widget2
------calling widget's introduce method for widget1 (widget2)
----------[widget1] name 
----------returning widget1's name value (Widgeter)
----------[widget1] widget_number 
----------returning widget1's widget_number value (1)
Hi, I'm Widgeter, widget #1.
----------[widget] name 
----------returning widget2's widget_number value (2)
Hi, I'm Widgetest, widget #2.
----------[widget] name
----------returning widget2's name value (Widget Class)
My parent is Widget Class.
----------[widget1] name
----------returning widget2's name value (Widgeter)
Please meet my friend, Widgeter.

... Why?!

I figured I'd keep trying until I hit the point where it was impossible, and that never happened.