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Increase 1 space after period (dot) to 2 but not more in vim

I am working on a simple text file in vim where I want to end every sentence with 2 spaces after full stop (dot/period). However, I do not want those sentences which already have 2 spaces after full stop to have further increase in spaces. The test text could be: 

This sentence has only 1 space after it. This one has two.  This line has again 1 space only. This is last line.

I tried: 

%s/\. /\.  /g

but this increases all spaces by one. I tried following also but it does not work: 

%s/\.  \\([^ ]\\)/.  \\1/g

How can I achieve this in vim?

Solution

  • You may use

    %s/\. \( \)\@!/.  /g

    The \. \( \)\@! pattern matches a . and a space that is not followed with another space.

    The (...)@! is a negative lookahead construct in Vim. See Lookbehind / Lookahead Regex in Vim. In other common regex flavors, it is written as (?!pattern). You may learn more about how negative lookaheads work in this answer of mine.

    To match any whitespace, replace the literal space with \s inside the pattern.