chapters/27.markdown @ 436f8ce22479

String Functions
================

Vim has many built-in functions to manipulate strings.  In this chapter we'll
look at a few of the most important ones.

Length
------

The first function we'll look at is `strlen`.  Run the following command:

    :::vim
    :echom strlen("foo")

Vim displays "3", which is the length of the string "foo".  Now try the
following command:

    :::vim
    :echom len("foo")

Vim once again displays "3".  When used with Strings `len` and `strlen` have
identical effects.  We'll come back to `len` later in the book.

Splitting
---------

Run the following command (note that it's an `echo` and not an `echom`):

    :::vim
    :echo split("one two three")

Vim displays `['one', 'two', 'three']`.  The `split` function splits a String
into a List.  We'll talk about Lists shortly, but for now don't worry too much
about them.

You can also tell Vim to use a separator other than "whitespace" for splitting.
Run the following command:

    :::vim
    :echo split("one,two,three", ",")

Vim will once again display `['one', 'two', 'three']`, because the second
argument to `split` tells it to split the string on the comma character instead
of on whitespace.

Joining
-------

Not only can you split strings, you can also join them.  Run the following
command:

    :::vim
    :echo join(["foo", "bar"], "...")

Vim will display "foo...bar".  Don't worry about the list syntax for now.

`split` and `join` can be paired to great effect.  Run the following command:

    :::vim
    :echo join(split("foo bar"), ";")

Vim displays "foo;bar".  First we split the string "foo bar" into a list, then
we joined that list together using a semicolon as the separator.

Lower and Upper Case
--------------------

Vim has two functions to change the case of Strings.  Run the following
commands:

    :::vim
    :echom tolower("Foo")
    :echom toupper("Foo")

Vim displays "foo" and "FOO".  This should be pretty easy to understand.

In many languages (like Python) a common idiom is to force strings to lowercase
before comparing them to perform a case-insensitive comparison.  In Vimscript
this isn't necessary because we have the case-insensitive comparison operators.
Reread the chapter on comparisons if you don't remember those.

It's up to you to decide whether to use `tolower` and `==#`, or just `==?` to
perform case-sensitive comparisons.  There doesn't seem to be any strong
preference in the Vimscript community.  Pick one and stick to it for all of your
scripts.

Exercises
---------

Run `:echo split('1   2')` and `:echo split('1,,,2', ',')`.  Do they behave the
same?

Read `:help split()`.

Read `:help join()`.

Read `:help functions` and skim the list of built-in functions for ones that
mention the word "String".  Use the `/` command to make it easier (remember,
Vim's help files can be navigated like any other kind of file).  There are
a *lot* of functions here, so don't feel like you need to read the documentation
for every single one.  Just try to get an idea of what's available if you need
it in the future.