#! /usr/bin/perl
use warnings;
use strict;
use utf8;
my $string = 'שָׁלוֹם';
print $string =~ /\bש/, "\n";

(I had to use <pre> instead of <code> to make UTF-8 work.)

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]

Given your strings, they match fine with or without \b:

#!/usr/bin/perl -CS
use HTML::Entities;
my $string = decode_entities <DATA>;
   $_      = decode_entities "&#1513;&#1508;&#1497;&#1512;&#1488;";
print "matches: '$&'\n"     if $string =~ /$_/;
print "matches too: '$&'\n" if $string =~ /\b$_\b/;
__DATA__
8^1589-20170113-102647-&#1493;&#1497;&#1495;&#1497;-&#1491;&#1489;&#15
+12;&#1497;_&#1492;&#1505;&#1508;&#1491;_&#1506;&#1500;_&#1492;&#1512;
+&#1489;_&#1502;&#1513;&#1492;_&#1513;&#1508;&#1497;&#1512;&#1488;.mp3
+^&#1506;&#1489;&#1512;&#1497;&#1514;^&#1492;&#1512;&#1489; &#1502;&#1
+504;&#1513;&#1492; &#1490;&#1493;&#1500;&#1491;^&#1493;&#1497;&#1495;
+&#1497;-&#1491;&#1489;&#1512;&#1497; &#1492;&#1505;&#1508;&#1491; &#1
+506;&#1500; &#1492;&#1512;&#1489; &#1502;&#1513;&#1492; &#1513;&#1508
+;&#1497;&#1512;&#1488;, &#1496;&#1493;' &#1496;&#1489;&#1514;, &#1514
+;&#1513;&#1506;'&#1494;^&#1513;&#1497;&#1506;&#1493;&#1512;&#1497;&#1
+501; &#1489;&#1514;&#1504;"&#1498; &#1493;&#1489;&#1508;&#1512;&#1513
+;&#1514; &#1492;&#1513;&#1489;&#1493;&#1506;|&#1513;&#1497;&#1506;&#1
+493;&#1512;&#1497;&#1501; &#1489;&#1508;&#1512;&#1513;&#1514; &#1492;
+&#1513;&#1489;&#1493;&#1506;|&#1513;&#1497;&#1506;&#1493;&#1512;&#149
+7;&#1501; &#1511;&#1493;&#1491;&#1502;&#1497;&#1501;|&#1489;&#1512;&#
+1488;&#1513;&#1497;&#1514;|&#1493;&#1497;&#1495;&#1497;
__END__
[download]

Output:

matches: 'שפירא'
matches too: 'שפירא'

So, no issue with \b and unicode regex here.

Thanks a lot, Monks.

Knowing that there's no issue wuth \b, I kept investigating. Turned out that one of the strings wasn't really utf8 (for some reason, my terminal insisted on printing it as utf8, though). utf8::decode solved the problem.

You actually had the opposite problem: You had UTF-8, but the regex engine expects a string of Unicode Code Points^[1]. utf8::decode provides the latter from the former.

---

1. More specifically, it's \w, \b, \d, etc that are defined in terms of UCP.