That is useful sometimes, but here it's not needed, because a lookahead is enough.

Run this: 

use warnings;
$sentence='kinase inhibitor SET6 activates p16(INK4A) in cell-wall.';
my @phrases = ('kinase i', 'inhibitor', 'tor SET6', 'SET6', 'p16(INK4A
+)', 'cell');
my $phrases_re = join '|', map { quotemeta } @phrases;
$sentence =~ s/(^| )($phrases_re)(?= |$)/$1#$2#/g;
print $sentence, "\n";

[download]

You get the output 

kinase #inhibitor# #SET6# activates #p16(INK4A)# in cell-wall.

[download]

Update: There are ways to do this kind of thing without lookaheads or lookbehinds, just as a curiosity. Replace the substitution statement above with either 

$sentence =~ s/(^| )($phrases_re)( |$)/$1#$2#$3/g for 0, 1;

[download]
or 
use 5.010; given ($sentence) { s/ /  /g; s/(^| )($phrases_re)( |$)/$1#
+$2#$3/g; s/  / /g; }

[download]

Update: One more alternative is below. 

my %phrase; $phrase{$_}++ for @phrases;
my @sentence = split /( +)/, $sentence;
for (@sentence) { $phrase{$_} and $_ = "#" . $_ . "#"; };
$sentence = join "", @sentence;

[download]

Update: Oh, let's not forget this one either. 

$sentence =~ s/(?<![^ ])($phrases_re)(?= |$)/#$1#/g;

[download]

In reply to Re^4: phrase match by ambrus
in thread phrase match by newbio

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.