Insert line numbers

==Using Vim==
The [[Search and replace|:s]] command can be used to insert line numbers before each line:
<pre>
:%s/^/\=printf('%-4d', line('.'))
</pre>

The pattern <code>^</code> matches the start of every line, and the replacement <code>\=</code> is the result of evaluating the following expression. That expression uses <code>printf()</code> to format the number of the current line: <code>%-4d</code> is a left-aligned decimal number, padded if necessary by adding spaces to a 4-column width (<code>%4d</code> is right-aligned, and <code>%04d</code> inserts leading zeroes).

To number a section, specify which lines should be numbered with a [[Ranges|range]]. For example, press <code>V</code> to select the first line, then press <code>j</code> to extend the selection down until all required lines are selected. Then type the following command (do not type <code>'<,'></code> as that is inserted by Vim):
<pre>
:'<,'>s/^/\=printf("%d.\t", line(".") - line("'<") + 1)
</pre>

The above example has a format string of <code>"%d.\t"</code> which inserts a left-aligned number, followed by a period and a tab character. Each line in the selected range is numbered. Use the following if you want to only number non-blank lines (it finds the start of a line followed by a character that is not whitespace):
<pre>
:'<,'>s/^\S/\=printf("%d.\t", line(".") - line("'<") + 1)
</pre>

In the above, blank lines are counted, but do not have a number inserted (the inserted numbers would be 1, 2, 3, 5, 6 if line 4 was blank).

The following alternative does not number blank lines and does not skip line numbers:
<pre>
:'<,'>g/^\S/s/^/\=printf("%d.\t", Inc())
</pre>

The above requires the <code>Inc()</code> function from [[Making a list of numbers|here]]. In addition, you need to set the value for the first line number before selecting any lines. To do that enter:
<pre>
:let i = 1
</pre>