chapters/50.markdown @ c639d2c11892
typo-the-then
Close branch.
author |
Steve Losh <steve@stevelosh.com> |
date |
Fri, 07 Oct 2016 13:11:30 +0000 |
parents |
ee7e65e9658e |
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Section Movement Theory
=======================
If you've never used Vim's section movement commands (`[[`, `]]`, `[]` and `][`)
take a second and read the help for them now. Go ahead and read `:help section`
as well.
Confused yet? That's okay, so was I the first time I read that stuff. We're
going to take a quick detour from writing code to learn about how these
movements work, and then in the next chapter we'll make our Potion plugin
support them.
Nroff Files
-----------
The four "section movement" commands are conceptually meant to move around
between "sections" of a file.
All of these commands are designed to work with [nroff files][] by default.
Nroff is a language like LaTeX or Markdown -- it's used to write text that will
be reformatted later (it's actually the format used by UNIX man pages).
Nroff files use a certain set of "macros" to define "section headings". For
example, here's an excerpt from the `awk` man page:
:::nroff
.SH NAME ***
awk \- pattern-directed scanning and processing language
.SH SYNOPSIS ***
.B awk
[
.BI \-F
.I fs
]
[
.BI \-v
.I var=value
]
[
.I 'prog'
|
.BI \-f
.I progfile
]
[
.I file ...
]
.SH DESCRIPTION ***
.I Awk
scans each input
.I file
for lines that match ...
The lines starting with `.SH` are section headings. I've marked them with
`***`. The four section movement commands will move your cursor between these
section heading lines.
Vim considers any line starting with `.` and one of the nroff heading macros to
be a section header, *even when you're not editing an nroff file*!
You can change the macros by changing the `sections` setting, but Vim still
requires a period at the beginning of the line, and the macros must be pairs of
characters, so that setting doesn't add enough flexibility for Potion files.
Braces
------
Section movement commands *also* look for one more thing: an opening or closing
curly brace (`{` or `}`) as the first character on a line.
`[[` and `]]` look for opening braces, while `[]` and `][` look for closing
braces.
This extra "hack" allows you to move between sections of C-like languages
easily. However, these rules are always the same no matter what type of file
you're in!
Put the following into a buffer:
:::text
Test A B
Test
.SH Hello A B
Test
{ A
Test
} B
Test
.H World A B
Test
Test A B
Now run `:set filetype=basic` to tell Vim that this is a BASIC file, and try the
section movement comments.
The `[[` and `]]` commands will move between the lines marked `A`, while `[]`
and `][` move between the lines marked `B`.
This shows us that Vim always uses these same two rules for section movement,
even for languages where neither one makes sense (like BASIC)!
[nroff files]: http://en.wikipedia.org/wiki/Nroff
Exercises
---------
Read `:help section` again, now that you know the story of section movement.
Read `:help sections` just for the fun of it.