Assuming lines are defined as sequences of non-newline characters terminated by newlines, it's just a matter of counting the number of newlines. Use the tr/// operator for that. 
my $nr_of_lines = $str =~ tr/\n//;

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Add 1 if you want to count an incomplete last line, and the string doesn't end with a newline.

In reply to Re: Count number of lines in a STRING by JavaFan
in thread Count number of lines in a STRING by danj35

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