Question

I am editing a Perl file, but I don’t understand this regexp comparison. Can someone please explain it to me?

if ($lines =~ m/(.*?):(.*?)$/g) { } .. 

What happens here? $lines is a line from a text file.

Answer 1

Break it up into parts:

$lines =~ m/ (.*?)      # Match any character (except newlines)
                        # zero or more times, not greedily, and
                        # stick the results in $1.
             :          # Match a colon.
             (.*?)      # Match any character (except newlines)
                        # zero or more times, not greedily, and
                        # stick the results in $2.
             $          # Match the end of the line.
           /gx;

So, this will match strings like ":" (it matches zero characters, then a colon, then zero characters before the end of the line, $1 and $2 are empty strings), or "abc:" ($1 = "abc", $2 is an empty string), or "abc:def:ghi" ($1 = "abc" and $2 = "def:ghi").

And if you pass in a line that doesn’t match (it looks like this would be if the string does not contain a colon), then it won’t process the code that’s within the brackets. But if it does match, then the code within the brackets can use and process the special $1 and $2 variables (at least, until the next regular expression shows up, if there is one within the brackets).