use warnings;
use strict;

my $string = " foo bar quz ";
print "String: '$string' length: ",length($string),"\n";

print "### Successful match with /c:\n";
pos($string)=undef;
print "<$1>\n" while $string =~ / \G \s* (foo|bar|quz) \s* /xgc;
print "pos: ",pos($string)//'undef',"\n";

print "### Failed match with /c:\n";
pos($string)=undef;
print "<$1>\n" while $string =~ / \G \s* (foo|bar) \s* /xgc;
print "pos: ",pos($string)//'undef',"\n";

print "### Successful match without /c:\n";
pos($string)=undef;
print "<$1>\n" while $string =~ / \G \s* (foo|bar|quz) \s* /xg;
print "pos: ",pos($string)//'undef',"\n";

print "### Failed match without /c:\n";
pos($string)=undef;
print "<$1>\n" while $string =~ / \G \s* (foo|bar) \s* /xg;
print "pos: ",pos($string)//'undef',"\n";

__END__

String: ' foo bar quz ' length: 13
### Successful match with /c:
<foo>
<bar>
<quz>
pos: 13
### Failed match with /c:
<foo>
<bar>
pos: 9
### Successful match without /c:
<foo>
<bar>
<quz>
pos: undef
### Failed match without /c:
<foo>
<bar>
pos: undef