How to define a command if the function needs to take an argument from the script itself?

Question

Suppose I am defining a few commands that are similar in functionality. In this particular case, I am defining a few commands that each echoes a particular message:

function! EchoMessage(text)
    echom text
endfunction

let thousand_chars = "天地玄黃，宇宙洪荒。日月盈昃，辰宿列張。 寒來暑往，秋收冬藏。閏餘成歲，律呂調陽 ..."
let lorem_ipsum = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, ..."
let brown_fox = "The quick brown fox jumps over the lazy dog."

command! ThousandCharacters call EchoMessage(thousand_chars)
command! LoremIpsum call EchoMessage(lorem_ipsum)
command! BrownFox call EchoMessage(brown_fox)

I have written it in this way to be able to reuse EchoMessage for many commands. Unfortunately, an error is produced when any of the commands (e.g. :LoremIpsum) are called, because vim will not provide text when EchoMessage is called using a command.

How can I structure my code so that the commands can make use of a common function (e.g. EchoMessage) with one argument provided in the script itself (e.g. brown_fox)?

Answer 1

The problem is that, in the body of your EchoMessage() function, text does not refer to the value passed in, but instead to a different local variable. Use a: to refer to parameters passed in:

echom a:text

See :help internal-variables (and specifically :help function-argument) for more details.