Unfortunately this would also match "TEST SENTENCE" (note the trailing whitespace).

The following test illustrates another method:

#!/usr/bin/perl -w

my $data = <<'EOF';
 This is a sentence. THIS \
IS A SENTENCE. This is \
a SEQUENCE OF UPPER WORDS and \
this is not.
EOF

while ( $data =~ m/(\b(?:[A-Z]+(?:\s+[A-Z]+)*)+\b)/g ) {
  print "Upper Sentence: \"$1\"\n";
}
[download]

Outputs:

Upper Sentence: "THIS IS A SENTENCE"
Upper Sentence: "SEQUENCE OF UPPER WORDS"
[download]

Somewhat simpler:

print "'$1'" while $data =~ m/(\b[A-Z][A-Z\s]+[A-Z]\b)/g;;
'THIS
IS A SENTENCE'
'SEQUENCE OF UPPER WORDS'
[download]

or

print "'$1'" while $data =~ m/(\b[A-Z][A-Z\s]+[^ ]\b)/g;;
'THIS
IS A SENTENCE'
'SEQUENCE OF UPPER WORDS'
[download]

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

The issue I have with your examples, BrowserUk, is that you are mandating at least 2 upper case letters. My regexp permits a single capital letter.

I think it is important to have the optional section, because the desired expression is "one or more upper case letters" optionally followed by any number of "spaces followed by upper case letters".

I may be wrong but I'm guessing from the backslashes in your heredoc that you want $data to contain a single-line string. I don't think what you have written will achieve that. Single quotes result in literal backslashes along with the newlines in the string and double quotes don't seem to escape the meaning of the newline. Doing a global substitution is one way of getting a single line. Consider the following code

use strict;
use warnings;

my $rcSep = sub { return q{*} x 20 . qq{\n} };
print $rcSep->();

my $singleQuoted = <<'EOD';
Line 1\
Line 2\
Line 3
EOD
print $singleQuoted, $rcSep->();

my $doubleQuoted = <<"EOD";
Line 1\
Line 2\
Line 3
EOD
print $doubleQuoted, $rcSep->();

( my $transformed = <<'EOD' ) =~ s{\n+(?!\z)}{ }g;
Line 1
Line 2
Line 3
EOD
print $transformed, $rcSep->();
[download]

and its output

********************
Line 1\
Line 2\
Line 3
********************
Line 1
Line 2
Line 3
********************
Line 1 Line 2 Line 3
********************
[download]

I hope this is of interest.

Cheers,

JohnGG

Thou art wise brother BrowserUk. I was just about to comment that I see a lot of non-working solutions;-) Alas my votes for today are gone.