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What is the difference between doing :% [...] and :g [...]. Does g require a regex to filter out what lines to apply to, or does it apply to all lines if no regex is given? For example:

To insert a " at the beginning of every line:

:% normal!I"

I'm guessing the equivalent g command would be:

:g/./ normal!I"

So, does % essentially translate to:

/./ in a command?

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These two are not really the same. In your example, :g/./ normal!I" will only prepend non-empty lines with a ", but it will not prepend the " to empty lines, which the :%normal!I" will do.

Yes, :g always needs a pattern and only acts on the lines that match that pattern. If you use an empty pattern (//), Vim will reuse the last pattern you used in a previous search, :s or :g command.

A closer similar to the % range would be using :g/^/, which is a pattern that will match all lines, including empty ones.

Using :g will have other side effects not in %, since when you use a pattern it is then saved as the last used pattern, which also presents itself visually if you have 'hlsearch' enabled.

Also note that :g itself takes a range! You can use :10,20g/pattern/command to execute the command only on lines between 10 and 20 which also match the passed pattern. In fact, :g/^/ normal!I" is equivalent to :%g/^/ normal!I". In other words, :g defaults to the % range when one is not passed explicitly.

The % range is exactly equivalent to :1,$, the range of lines between the first and the last one in the buffer.

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    great answer, thank you very much for the clarification on the above.
    – David542
    Jun 21 '20 at 2:38
  • @David542 I tried to cover all angles 😁
    – filbranden
    Jun 21 '20 at 2:50
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One other subtlety not noted by filbranden, is that the manner in which the two commands process the set of lines is a little different. The simplest example of the difference is probably to compare these two commands:

:%join
:g/^/join

The first will concatenate every line in your buffer into a single line. The second will concatenate every other line to its adjacent line (so you end up with half as many lines as before).

:help :global explains why :g works in this way:

The global commands work by first scanning through the [range] lines and marking each line where a match occurs (for a multi-line pattern, only the start of the match matters).

In a second scan the [cmd] is executed for each marked line, as if the cursor was in that line. For ":v" and ":g!" the command is executed for each not marked line. If a line is deleted its mark disappears.

(emphasis mine)

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  • oh very interesting and good to know, thanks for the thorough explanation!
    – David542
    Jun 22 '20 at 16:30

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