I stumbled on this example atDoesn't say it's deprecated, though. Still, is there ever a time $1 won't work?
http://tutorials.findtutorials.com/read/category/80/id/99/p/
(bottom of the page)...
<snip>
Finally, in our tour of regular expressions, let's look again at backreferences. Suppose you want to find any repeated words in a string. How would you do it? You might think about doing this:
if (/\b(\w+) $1\b/) { print "Repeated word: $1\n";}
Except, this doesn't work, because $1 is only set when the match is complete. In fact, if you have warnings turned on, you'll be alerted to the fact that $1 is undefined every time. In order to match while still inside the regular expression, you need to use the following syntax:
if (/\b(\w+) \1\b/) { print "Repeated word: $1\n";}
However, when you're replacing, you'll get a warning if you try and use the \<number> syntax on the wrong side. It'll work, but you'll be told "\1 better written as $1 ".
</snip>
Tom
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