It sounds like you're just wanting to remove any periods that follow just one word character. I'm sure there might be a rare exception to this, but the following would accomplish that basic feat: 
use strict;
use warnings;

my $str = "a history of u.s. coast guard aviation.  M.C. Esher";

$str =~ s/(?<=\W\w)\.//g;

print $str, "\n";

[download]
I'd also be tempted to force capitalization on those abbreviations, but that might not be what you're after: 
# Remove periods and capitalize, so we have US instead of us.
$str =~ s/(?<=\W)(\w)\./\U$1/g;

[download]
- Miller

In reply to Re: Lookahead/Lookbehind Regular Expression... by wind
in thread Lookahead/Lookbehind Regular Expression... by mogmismo

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