@list = qw( this that other \w+\s\w+ );
$re = join '|', @list;
$re = qr/$re/;
print "Match\n" if 'foo bar' =~ m/$re/;

##</code><code>##

$re = join '|', map{quotemeta} @list;

##</code><code>##

my $re;
my $str = '(foo';
eval {$re = qr/$str/};
if ( $@ ) {
    print "Oops $@\n";
}
print "Still running.....$re\n";

$str = '/;print"You hacked me!";/';
eval {$re = qr/$str/};
if ( $@ ) {
    print "Oops $@\n";
}
print "Still running.....$re\n";

$str = '/;print"You hacked me!\n";/';
eval "\$re = qr/$str/";
if ( $@ ) {
    print "Oops $@\n";
}
print "Still running.....$re\n";
__DATA__
Oops Unmatched ( before HERE mark in regex m/( << HERE foo/ at C:\PROGRA~1\PERLBU~1\debug\test.pl line 5.

Still running.....
Still running.....(?-xism:/;print"You hacked me!";/)
*****You hacked me!
Still running.....(?-xism:)