Remove periods from the end of markdown paragraphs

Question

I have a bunch of posts written in markdown and I need to remove the periods from the end of every paragraph in each of them

The end of a paragraph in markdown is delimited by:

• 2 or more \ns or
• The end of the string

However, there are these edge cases

1. Ellipses
2. Acroynms (e.g., I don't want to drop the final period in "Notorious B.I.G." when it falls at the end of a paragraph). I think you can deal with this case by saying "don't remove the final period if it's preceded by a capital letter which is itself preceded by another period"
3. Special cases: e.g., i.e., etc.

Here's a regular expression that matches posts that have offending periods, but it doesn't account for (2) and (3) above:

/[^.]\.(\n{2,}|\z)/

Answer 1

(?<!\.[a-zA-Z]|etc|\.\.)\.(?=\n{2,}|\Z)

• (?<!\.[a-zA-Z]|etc|\.\.) - lookbehind to make sure that the period is not preceded by sequences like .T, etc, .. (for ellipsis).
• \. the period
• (?=\n{2,}|\Z) lookahead to look for end of a markdown paragraph (two newlines or end of string)

Test:

s = """ths is a paragraph.

this ends with an ellipsis...

this ends with etc.

this ends with B.I.G.

this ends with e.g.

this should be replaced.

this is end of text."""
print s.gsub(/(?<!\.[a-zA-Z]|etc|\.\.)\.(?=[\n]{2,}|\Z)/, "") 
print "\n"

Output:

this is a paragraph

this ends with an ellipsis...

this ends with etc.

this ends with B.I.G.

this ends with e.g.

this should be replaced

this is end of text

Answer 2

A Ruby 1.8.7 compatible algorithm:

s = %{this is a paragraph.

this ends with an ellipsis...

this ends with etc.

this ends with B.I.G.

this ends with e.g.

this should be replaced.

this is end of text.}.strip

a = s.split(/\n{2,}/).each do |paragraph|
  next unless paragraph.match /\.\Z/
  next if paragraph.match /(\.[a-zA-Z]|etc|\.\.)\.\Z/
  paragraph.chop!
end.join("\n\n")

>> puts a
this is a paragraph

this ends with an ellipsis...

this ends with etc.

this ends with B.I.G.

this ends with e.g.

this should be replaced

this is end of text