my $s1  = "abc";
my $s2  = "/abc";
my $all = "/abc";

print "OK1\n" if $all =~ /^$s1/;
print "OK2\n" if $all =~ /^$s2/;
print "OK3\n" if $all =~ /^\/?$s1/;
print "OK4\n" if $all =~ /^\/?$s2/;