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http://en.wikipedia.org/wiki/Palindrome

A palindrome is a word, phrase, number or other sequence of units that
has the property of reading the same in either direction (the
adjustment of punctuation and spaces between words is generally
permitted).


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Write a program that can find the longest single word palindrome in a
set of files.  The program should support being called with a list of
one or more input files:

  perl find-pal.pl in1.txt in2.txt in3.txt ...

An example input file (pal1.txt) might be:
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The most familiar palindromes, in English at least, are
character-by-character: the written characters read the same backwards
as forwards. Palindromes may consist of a single word (civic, level,
racecar, rotator, Malayalam), or a phrase or sentence ("Neil, a trap!
Sid is part alien!", "Was it a rat I saw?", "Mr. Owl ate my metal
worm", "Sit on a potato pan, Otis", "Rats live on no evil
star."). Spaces, punctuation and case are usually ignored.

The Guinness Book of Records gives detartrated, the past tense of
detartrate, a somewhat contrived chemical term meaning to remove
tartrates. Rotavator, a trademarked name for an agricultural machine,
is often listed in dictionaries. The term redivider (i.e. someone or
something that redivides) is used by some writers but appears to be an
invented term - only redivide and redivision appear in the "Shorter
Oxford Dictionary". Malayalam, an Indian language, is of equal length
(strictly, this name should be spelt either Malayaalam or
Malay\u0101lam, as the next to last vowel is long.) Another aspect of
the word "malayalam" is that it stays a letter palindrome if it is
written in any phonetic script like devnagari.
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When run as:

    perl find-pal.pl pal1.txt

Which should result in the output:

    Longest in inp1.txt => Malayalam
    Longest over all was: inp1.txt => Malayalam