use strict;
use warnings;
use Data::Dumper ();

die "No search terms supplied!" unless @ARGV;
my @words = @ARGV;

my $text = do { local $/ = undef; <DATA> };

my $blen = 20;	# (max) chars before a matching word to take with us
my $alen = 20;	# (max) chars after a matching word to take with us
my $jlen = $blen+$alen;	# (max) chars between 2 matching words captured together

my $strwords = join "|" => map quotemeta, @words; # Words to highlight
my $rxwords = qr/\b(?i:$strwords)\b/;	# ... compiled highlight word match
my $expr = qr/\b(?!\s)(?s:.{0,$blen}$rxwords(?:.{0,$jlen}$rxwords)*.{0,$alen}(?:(?<=\s)|[^\s]*\b))/;

my $D = Data::Dumper->new(
	[[grep {s/($rxwords)/[$1]/g} $text =~ /($expr)/g]], ['matched']
)->Indent(1);
print $D->Dump();

# reformatted the DATA to look nicer in the post
__DATA__
Regular expressions have always been a weak spot for me, and
I've got a question that's got me stumped.  Here's the
problem I'm trying to solve.  I have somewhat large articles
of text (returned from a search), what I'd like to do is
capture the word and X number of words before and after it
while tagging the matching word in the captured text.  My
inital thought was to try something like this.  The problem I
have is that if there is more than one term and they overlap,
the nth term will not be annotated.  So my next thought is
lookahead/lookbehind, but they don't capture.  Is there a way
to do this with a single regex?  Is a regex even the best way
to do this?  Thanks, -Lee

##</code><code>##

perl -Mstrict -Mwarnings context.pl is and the have
$matched = [
  'Regular expressions [have] always been a weak spot for me, [and]
I\'ve got a question',
  'me stumped.  Here\'s [the]
problem I\'m trying to solve.  I [have] somewhat large articles',
  'what I\'d like to do [is]
capture [the] word [and] X number of words before [and] after it
while tagging [the] matching word in [the] captured text.  My
',
  'like this.  [The] problem I
[have] [is] that if there [is] more than one term [and] they overlap,
[the] nth term will not be',
  'So my next thought [is]
lookahead/lookbehind',
  'don\'t capture.  [Is] there a way
to do this',
  'a single regex?  [Is] a regex even [the] best way
to do this'
];

##</code><code>##

\b              # a word boundary
(?!\s)          # following char is not a white space (1)
(?s:            # . matches newline in rest of regex
  .{0,$blen}    # up to $blen chars (left context)
  $rxwords      # followed by a word we search for
  (?:           # group for repeatedly matching
    .{0,$jlen}  #   up to $jlen=$blen+$alen chars (2)
    $rxwords    #   followed by a searched word
  )*            # repeatedly match
  .{0,$alen}    # up to $alen chars (right context)
  (?:           # group for disjunction (3)
    (?<=\s)     #    last matched char was white space
   |            #  or
    [^\s]*      #    non white space chars
    \b          #    up to the next word boundary
  )
)