Some programmers are extremely sensitive about formatting. Perfectionists, sticklers, pedants -- call them what you will, they'll always be there to reformat entire source files to confuse an otherwise comprehensible Git history. Admittedly, I do like source files to be perfectly formatted, even down to whitespace. Even if you're completely relaxed about source formatting, you'll still need to master the basics of Vim's built-in indentation capabilities.

Configuring Indentation

The expandtab option causes Vim to insert with spaces instead of tabs. The exact number of spaces can be set using softtabstop. The shiftwidth should also be set because this controls how many spaces will be used with autoindent.

The average .vimrc might look like this:

set expandtab
set shiftwidth=2
set softtabstop=2

If you're working with tabs then the number of spaces used to visually represent the tab character can be set with tabstop.

Two characters usually appeals to Ruby and certain JavaScript developers. If you work with both Ruby and Python, then you may like to use autocmd to change the settings based on the current file's language:

autocmd FileType python setlocal expandtab shiftwidth=4 softtabstop=4

The setlocal only applies the setting to the current buffer or window. That means Vim is easily capable of handling settings for multiple file types at the same time.

Automatic Indentation

By setting autoindent, Vim will add indentation as lines of code are entered. Although most people seem content with this setting, it's actually very simple -- it just copies the indentation level from the previous line.

Conversely, smartindent is triggered when starting a new line. Various languages are supported, and I find it works well for the languages I use on a daily basis.

These options can be disabled by adding no: set noautoindent. They're also aliased to shorter commands:

set ai
set noai
set si
set nosi

Reformatting Commands

The = command will format lines based on a motion. It also works with Visual mode:

• =5j: Format five lines
• CTRL-V, select lines, =: indent the selected lines. This also works with the mouse if mouse input has been configured

Vim will use its internal formatting function unless indentexpr has been specified. Some languages have specific rules for formatting, so people write indentation files for Vim to better support them.

If a line needs to be indented, then pressing >> will indent it, and << will do the reverse. A motion can be supplied as well, so >3j will indent the next three lines. I find visually selecting a line then using > very useful, because it accepts a count argument: CTRL-V, make selection, 2> will indent two levels over the selection.