When you tried: 

$script=~s/(\W)/_/g;

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you're actually replacing every none word character with an underscore. hence your filename "cos.NEW&OLD.0826.12345" would become "cos_NEW_OLD_0826_12345" which is obviously cumbersome to write, just in case. If you want everything remain the way it is, just escape the metacharacter itself. 
my $script = "cos.NEW&OLD.0826.12345";
$script=~s/\&/_/;
print "$script";    #outputs "cos.NEW_OLD.0826.12345"

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NOTE:Regular expression are not as consternating as they may seem!, invest the time at learning them effectively and you would see it coming your way easier than the head-whirlpool I used to suffer from when I did not know nothing about regexes, Now at least I can analyse and correlate them better. See it for yourself :)

Excellence is an Endeavor of Persistence. Chance Favors a Prepared Mind.

In reply to Re: Removing a Metacharacter from a filename by biohisham
in thread Removing a Metacharacter from a filename by sputnik

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