How do I run a global command only on lines within a visual selection?

Explanation

How it works

The :g (global) command is one of Vim's most powerful features. It matches lines by a pattern and runs an Ex command on each matching line. By combining it with a visual selection range, you restrict its operation to only the selected lines.

The syntax is:

:'<,'>g/pattern/command

• '<,'> - The visual selection range (auto-filled when pressing : in visual mode)
• g/pattern/ - Match lines containing pattern
• command - The Ex command to run on each matching line

Common use cases:

• :'<,'>g/DEBUG/d - Delete all lines containing "DEBUG" in the selection
• :'<,'>g/^$/d - Delete all blank lines in the selection
• :'<,'>g/TODO/normal A (DONE) - Append " (DONE)" to lines containing "TODO"
• :'<,'>g!/important/d - Delete lines NOT containing "important" (inverse match with g! or v)
• :'<,'>g/error/s/warn/error/g - On lines matching "error", run a substitution

The inverse variant :v/pattern/command (or :g!/pattern/command) runs the command on lines that do NOT match the pattern.

Example

Given this log file, with lines 2-6 selected:

[INFO] Starting app
[DEBUG] Loading config
[INFO] Config loaded
[DEBUG] Connecting to DB
[INFO] Connected
[DEBUG] Running query
[INFO] Shutdown

1. Select lines 2 through 6 with V4j
2. Type :'<,'>g/DEBUG/d and press Enter

Result:

[INFO] Starting app
[INFO] Config loaded
[INFO] Connected
[INFO] Shutdown

Only DEBUG lines within the selection were removed. Lines outside the selection were untouched, including the first and last INFO lines.