How do I swap two adjacent words on a line using a substitute command in Vim?

Explanation

By using capture groups in a substitute command with very magic mode (\v), you can swap two adjacent words in a single operation. This technique is useful for quickly reversing argument order, fixing word transpositions, or restructuring identifiers.

How it works

• :s/ — Starts a substitute on the current line.
• \v — Enables very magic mode: parentheses and + have special meaning without backslashes, making the pattern more readable.
• (\w+) — Captures the first word (letters, digits, and underscores).
• \s+ — Matches one or more whitespace characters separating the two words.
• (\w+) — Captures the second word.
• /\2 \1/ — Replacement: second captured group, a space, first captured group.

Example

Before: foo bar
After:  bar foo

Swap function arguments (keeping the separator):

:s/\v(\w+),\s*(\w+)/\2, \1/

Before: move(width, height)
After:  move(height, width)

Tips

• Add the g flag to swap every adjacent word pair on the line: :s/\v(\w+)\s+(\w+)/\2 \1/g
• Use :%s/... to apply to the whole file.
• Without \v, escape the parentheses: :s/\(\w\+\)\s\+\(\w\+\)/\2 \1/
• To swap only within a visual selection: :'<,'>s/\v(\w+)\s+(\w+)/\2 \1/