How can I a put a line like “==========” quickly in vim

Question

I am editing restructuredtext files. I often need to put some charactors like \"=-`~\" in one line, and I want the length of the line match the previous line. How should I

Answer 1

If your line starts without any trailing whitespace:

Hello World    

Normal Mode:

YpVr=

Gives:

Hello World
===========

Explanation

Y -> Yank entire line, like yy
p -> paste the line
V -> select whole line in visual line mode r -> replace all of select with next character
= -> the character to replace the others

If you line has leading whitespace, eg:

    Hello World

Use:

Ypv$r=

Giving:

    Hello World
    ===========

We use v$ visual selection to the end of the line, rather than using V to select everything on the line.

If you had trailing whitespace you can use the g_ movement to get to the last non whitespace character.