Sure. The scalar range operator (or flip-flop) is one of the lesser-used features of Perl. perldoc perlop describes its behavior:
The operator is bistable, like a flip-flop, and emulates the line-range (comma) operator of sed, awk, and various editors. Each ".." operator maintains its own boolean state. It is false as long as its left operand is false. Once the left operand is true, the range operator stays true until the right operand is true, AFTER which the range operator becomes false again.
...
The value returned is either the empty string for false, or a sequence number (beginning with 1) for true. The sequence number is reset for each range encountered.
For your case, $flip effectively counts the repeated words, starting at 1 when a word matches prevword, and ending when a word does not match prevword. So $flip will be 1 for the first repeated word, 2 for the next repetition, etc. When it encounters a new word, it will be return whatever the count is, appended with E0 to indicate that it's finished the run. Like 5E0.

You can see its behavior in your own code by simply printing $flip after it is set.

Caution: Contents may have been coded under pressure.

In reply to Re^4: removing repeats by Roy Johnson
in thread removing repeats by dummy2

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