my @words = $_ =~ m/\b[A-Z]+\b/g;

Aren't you missing capturing brackets there?

my @words = m/\b([A-Z]+)\b/g;
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foreach(@words) { $acronyms_captured{$_} = undef; }

Personally, I'd write that as:

@acronyms_captured{@words} = ();
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I like hash slices a lot :-)

well, i thought it didnt matter in this case either way as whatever is captured here is what i want ... but i guess adding capturing brackets to make it explicit is better practise.
... and also the same with using ( ) for undef
am learning ... thanks

Thanks a lot, but I don't understand the line

my @words = $_ =~ m/\b[A-Z]+\b/g;
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You don't use split ?

Thanks a lot, but I don't understand the line  my @words = $_ =~ m/\b[A-Z]+\b/g;

I used regular expressions here to capture all consecutively appearing upper case alphabets separated by word boundaries (\b). Please check the perl regular expressions documentation

You don't use split ?

You could use split if you like but i think it is better to split by \W+ (non-word character) rather than \s+. This helps keep pattern matching simple in the next step. For the sample text below, using \s+ instead of \W+ would find none unless we perform a more complicated pattern matching later.

my %acronyms;

my $text= "An important class of transcription factors called general 
+transcription factors (GTF) are necessary for transcription to occur.
+ The Most common GTF's are TFIIA, TFIIB, and TFIIE.And a few more not
+ mentioned here.";

my @words = split('\W+', $text);

foreach(@words) {
       if($_ =~ m/^[A-Z]+$/){ $acronyms{$_}++; }
}
foreach( keys(%acronyms) ){ print "$_ seen $acronyms{$_} times\n"; }
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