Also don’t overlook the possibility of using a command-line utility. For example, the egrep -c regex_pattern utility is available in Unix/Linux land, and comparable facilities are finally also available in Windows PowerShell.
Use care in building your regex. For example, do you or do you not want to count lines which contain only a plus-sign in the first position, i.e. followed directly by end-of-line rather than a space? It will be a really good idea to construct a very short test-file, four or five lines long, which will thoroughly exercise all of the possibilities that you are (and are not ...) looking for, and whose right-answers are known in advance. Carefully consider every “edge case,” and include them in your test-data file. “Trust, but Verify.” Write the command-line (or the Perl), then prove that it works.