I copied this code from the tutorial page but it doesn't work. Tutorial by Roy Johnson. Perhaps my $_ is wrong. I just want to capture "a". Any ideas? 
use English;
$_ = "foo a baz bar";

/foo       # Match starting at foo
 (?:       # Complex expression:
   (?!baz) #   make sure we're not at the beginning of baz
   .       #   accept any character
 )*        # any number of times
 bar       # and ending at bar
/x;

print "$_ \n";
print "  \$1 = $1 \n";
print "  \$2 = $2 \n";
print "  \$& = $MATCH \n";
print "  \$` = $PREMATCH \n";
print "  \$' = $POSTMATCH \n";
print "  \$+ = $LAST_PAREN_MATCH \n";

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In reply to Regex look ahead by pglenski

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