What does g mean in Vim?

In Vim, g refers to the global command, an extremely powerful and versatile feature used to execute an Ex command on every line that matches a specified pattern throughout a file.

Understanding the Global Command (:g)

The global command, invoked as :g, allows users to perform operations on multiple lines simultaneously, making it indispensable for advanced text manipulation and refactoring tasks. Its core function is to first identify lines matching a regular expression and then apply a subsequent command to each of those identified lines.

Syntax and Operation

The general syntax for the global command is:

:g/{pattern}/{command}

• {pattern}: This is a regular expression (regex) that Vim uses to search for lines. Only lines that contain a match for this pattern will be processed.
• {command}: This is an Ex command (also known as a command-line mode command) that will be executed on each line identified by the {pattern}.

Practical Examples and Insights

The flexibility of the :g command comes from its ability to combine with various patterns and commands:

• Targeting Non-Empty Lines: A common and useful pattern is /./. This regular expression matches any line that contains at least one character, effectively targeting all "non-empty lines" in your file. For instance, lines containing text like "const" or "console" would be matched, while completely blank lines would be ignored.
• Executing Normal Mode Commands: You can run Normal mode commands on matched lines by using the :normal Ex command. For example, :g/{pattern}/normal A; would append a semicolon (;) to the end of every line that matches {pattern}. Here, A moves to the end of the line and enters insert mode, and ; is the character inserted before Vim automatically returns to Normal mode.

Here are more common applications of the global command:

• Deleting Specific Lines:
  • :g/Error/d: Deletes every line that contains the word "Error".
  • :g/^\s*$/d: Deletes all entirely empty or whitespace-only lines.
• Commenting Out Lines:
  • :g/^/normal I//: Inserts // at the very beginning of every line in the file, effectively commenting them out for many programming languages.
• Appending or Prepending Text:
  • :g/function/normal A;: Appends a semicolon to the end of every line that contains the word "function".
• Substituting Text Globally (on matching lines):
  • :g/todo/s//DONE/g: First, it finds all lines containing "todo". Then, on each of those lines, it substitutes all occurrences of "todo" with "DONE". This differs from a simple :%s/todo/DONE/g which would perform the substitution on every line.

Related Commands

The global command often works in conjunction with or has a complementary command:

By mastering the :g command and its variations, Vim users can achieve remarkable efficiency in managing and transforming text, making it a cornerstone for productive development and content creation workflows.