What's wrong with \b? It's only needed at the beginning, since you have the closing quote to mark the end. (UPDATED below with fancier pattern)

Test code: 

#!/usr/bin/perl
use strict;
use warnings;
use diagnostics;

my $alpha = qq(alpha="first");
my $beta  = qq(beta="second");
my $gamma = qq(gamma="third");

my $s1 = qq($alpha $beta $gamma);
my $s2 = qq($alpha $gamma $beta);
my $s3 = qq($beta $alpha $gamma);

#my $pat = qr/\b(beta="second")/;
my $pat = qr/(?:\A|\s)(beta="second")(?:\s|\Z)/;

print "s1: \'$s1\', match=".($s1 =~ $pat ? $1 : "nada")."\n";
print "s2: \'$s2\', match=".($s2 =~ $pat ? $1 : "nada")."\n";
print "s3: \'$s3\', match=".($s3 =~ $pat ? $1 : "nada")."\n";

[download]
Produces: 
s1: 'alpha="first" beta="second" gamma="third"', match=beta="second"
s2: 'alpha="first" gamma="third" beta="second"', match=beta="second"
s3: 'beta="second" alpha="first" gamma="third"', match=beta="second"

[download]
Updated: Removed half the test cases, since there's really only 3 possibilities. Also added fancy pattern that ensures either start/end of string or space is present.

In reply to Re: match whitespace or beginning/end of string by gmargo
in thread match whitespace or beginning/end of string by azadian

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