Vim .gitignore template

The bracket patterns look cryptic until you know what they are for. When Vim opens a file it creates a swap file holding unsaved changes, named after the original with a .swp extension. If that name is taken, because a second session is editing the same file, it uses .swo, then .swn, and continues backwards through the alphabet. The character ranges catch the whole family in a few lines instead of thirty.

The leading [._] in each pattern covers both naming conventions. A swap file for foo.txt is normally .foo.txt.swp with a leading dot, but with certain settings it is foo.txt.swp instead, so both forms need matching. The bracket is doing the same job the ranges do further along the line: collapsing a family of similar names into one rule instead of listing every possible variant.

!*.svg is the negation that stops the range patterns from doing damage. The pattern [._]*.s[a-v][a-z] would otherwise match a filename ending in .svg, because s, v and g fall inside those ranges. Without the negation, an entire directory of vector graphics would silently vanish from a repository, which is a memorable way to learn how character classes work.

Session.vim and Sessionx.vim are saved sessions: which files were open, which windows were split, where the cursor sat. They are a snapshot of one person's workspace and they contain absolute paths. [._]*.un~ files are the persistent undo history, which stores the full edit history of a file so undo survives closing the editor, and which therefore contains text you deleted and never committed.

tags is the index file that ctags generates for jump to definition. It is derived from the source, it is large, and it goes stale immediately, so regenerating it is always cheaper than merging someone else's copy. .netrwhist is the history of directories visited in the built in file browser.