How do I transform text in a visual selection using awk or sed?

Explanation

Vim can pipe any visual selection through external Unix commands and replace the selection with the output. Using awk, sed, sort, tr, or any command-line tool lets you perform transformations that would be complex in pure Vimscript.

How it works

• Select text in visual mode (v, V, or <C-v>)
• ! — triggers the filter command
• The selection is sent to the command's stdin
• The command's stdout replaces the selection

Example

:'<,'>!awk '{print toupper($0)}'

Before:
hello world
foo bar

After:
HELLO WORLD
FOO BAR

Reverse field order:

:'<,'>!awk '{print $2, $1}'

Tips

• Use sed for substitutions: :'<,'>!sed 's/old/new/g'
• Chain commands with pipes: :'<,'>!sort | uniq -c | sort -rn
• Use tr for character transforms: :'<,'>!tr '[:lower:]' '[:upper:]'
• Press u to undo if the result isn't what you expected