How do I programmatically manipulate register contents using setreg and getreg?

Explanation

How it works

Vim provides two functions for advanced register manipulation: setreg() and getreg(). These let you read, modify, and set register contents programmatically, including controlling the register type (characterwise, linewise, or blockwise).

The setreg() function takes three arguments:

• Register name (a single character as a string)
• The new contents (a string or list of strings)
• The register type: 'c' for characterwise, 'l' for linewise, 'b' for blockwise

The getreg() function retrieves register contents:

• getreg('a') -- get contents as a string
• getreg('a', 1, 1) -- get contents as a list of lines
• getregtype('a') -- get the register type

Using @a in expressions is shorthand for getreg('a').

Example

Append text to a register with a separator:

:call setreg('a', @a . "\n---\n" . @b, 'l')

This concatenates register a, a separator line, and register b, then stores the result back in register a as linewise text.

Convert a characterwise register to blockwise:

:call setreg('a', getreg('a'), 'b')

Set a register to a list of lines (creating a linewise register):

:call setreg('a', ['line1', 'line2', 'line3'], 'l')

Modify register contents with a substitution:

:call setreg('a', substitute(@a, 'old', 'new', 'g'))

These functions give you full control over registers that simple yank and paste commands cannot achieve, enabling complex text processing workflows.