"L F"
"LF"
"L.F"
"L. F"
"HTML"
"XML"
"X.H.T.M.L"
"X. H. T. M. L"
"X H T M L"

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;
$|=1;

while (my $line = <DATA>)
{
   next if $line =~ /^\s*$/;  #skip blank lines
   $line =~ s/\s*$//;         #delete line endings
   
   print "INPUT LINE: \'$line\'\n";
   $line =~ s/\s+|\,|\.//g; #remove spaces, commas, periods
  
   my @acron = $line =~ m/([A-Z]{2,})/g; #get sequence of 2 or 
                                         #more uppercase chars
   print "Acronym $_\n" for @acron;
}

=Prints
INPUT LINE: 'L F and LF and L.F. and L. F. and not L, F.'
Acronym LF
Acronym LF
Acronym LF
Acronym LF
Acronym LF
INPUT LINE: 'some HTML some XML.'
Acronym HTML
Acronym XML
INPUT LINE: 'or X.H.T.M.L. or X. H. T. M. L. or even X H T M L'
Acronym XHTML
Acronym XHTML
Acronym XHTML
INPUT LINE: 'but not U and I,'
INPUT LINE: 'or You and I.'
INPUT LINE: '...'
=cut

__DATA__
L F and LF and L.F. and L. F. and not L, F.
some HTML some XML.
or X.H.T.M.L. or X. H. T. M. L. or even X H T M L
but not U and I,
or You and I.
...