A stack? In bash?

For reasons I won’t go into here, I needed a simple stack implementation. In bash.

Now, stack implementations aren’t difficult, and bash does have arrays. But bash does not have classes or objects, and I wanted a general-purpose solution, not a quick-and-dirty, one-use hack.

The specification

The specification for my stack implementation is simple and straightforward. I wanted the following functions:

• stack_new name: Create a stack with the specified name. The name is akin to variable name and follows the same naming conventions.
• stack_push name value ...: Push one or more values onto the stack called name.
• stack_pop name variable: Pop the top value from the stack called name, storing the result in the named variable.
• stack_destroy name: Destroy the stack called name
• stack_size name variable: Store the size of the stack called name in the specified variable.
• stack_print name: Display the contents of the stack called name on stdout.

I didn’t bother with stack_clear, since stack_destroy followed by stack_create is good enough. It’d be simple enough to add a stack_clear function, though.

Example

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stack_new foo
stack_push foo 10 20 30
stack_print foo          # prints: ( 30 20 10 )
stack_pop foo i          # i is now 30. Stack is now ( 30 20 )

The implementation

The implementation is, to put it bluntly, rather ugly. But, as my first boss (many years ago) was fond of saying, “If the solution has to be ugly, at least hide the ugly.” The ugly is hidden in the implementation, where I don’t have to look at it.

So, without further ado, here’s the code:

The code is also checked into my GitHub lib-sh repository, as stack.sh.