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Chapter 2. Extended Introductory ExamplesRemember the doubled-word problem from the first chapter? I said that a full solution could be written in just a few lines in a language like Perl. Such a solution might look like: $/ = ".\n"; while (< >) { next if !s/\b([a-z]+)((?:\s|<[^>]+>)+)(\1\b)/\e[7m$1\e[m$2\e[7m$3\e[m/ig; s/^(?:[^\e]*\n)+//mg; # Remove any unmarked lines. s/^/$ARGV: /mg; # Ensure lines begin with filename. print; } Yup, that's the whole program. Even if you're familiar with Perl, I don't expect you to understand it (yet! ). Rather, I wanted to show an example beyond what egrep can allow, and to whet your appetite for the real power of regular expressions. Most of this program's work revolves around its three regular expressions:
Though this is a Perl example, these three regular expressions can be used verbatim (or with only a few changes) in many other languages, including Python, Java, Visual Basic .NET, Tcl, and more. Now, looking at these, that last
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