How do I define a custom Ex command that can accept a line range or count like built-in Vim commands?

Explanation

Custom Ex commands defined with :command -range can be called with a line range (e.g., '<,'>MyCmd or 1,10MyCmd) just like built-in commands such as :sort or :delete. Inside the command body, <line1> and <line2> hold the first and last line of the range, and <count> holds the line count. This lets you build powerful domain-specific shortcuts that operate on ranges without plugins.

How it works

• -range accepts the default range of the current line (.)
• -range=% defaults to the whole file if no range is given
• -range=N uses count N as a default
• <line1>, <line2> interpolate the actual range boundaries in the body
• Use <count> when you want a count rather than a range (mutually exclusive with <line1>/<line2>)

Example

Define a :Trim command that removes trailing whitespace from a range:

:command -range Trim <line1>,<line2>s/\s\+$//e

Now you can use it in multiple ways:

:Trim          " trims the current line
:%Trim         " trims the entire file
:'<,'>Trim     " trims the visual selection
:5,20Trim      " trims lines 5 to 20

Tips

• Add -nargs=* to also accept arguments: :command -range -nargs=* MyCmd ...
• Use <q-args> to pass the raw argument string, <f-args> to split on whitespace into a list
• Add ! to allow overwriting an existing command: :command! -range Trim ...
• Put the definition in your vimrc so it's always available