How do I prevent duplicate autocommands when reloading vimrc?

Explanation

Using augroup with autocmd! inside prevents duplicate autocommands from accumulating when you reload your vimrc.

How it works

• augroup name starts a named group
• autocmd! clears all autocommands in the group
• Define new autocommands
• augroup END closes the group

Example

augroup MyGroup
    autocmd!
    autocmd BufWritePre * :%s/\s\+$//e
    autocmd FileType python setlocal tabstop=4
augroup END

Tips

• Without augroup + autocmd!, each :source ~/.vimrc adds duplicates
• Name groups descriptively
• Each group can contain multiple autocommands
• autocmd! at the start of the group clears the old ones
• This is the standard pattern for vimrc autocommands