erb: multiline anchors

* bin/erb (ARGV.switch, ERB::Main#run): use beginning/end of
  string anchors instead of beginning/end of line anchors.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47994 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Author: nobu

bin/erb

@@ -11,7 +11,8 @@ class ERB
       return nil if self.empty?
       arg = self.shift
       return nil if arg == '--'
-      if arg =~ /^-(.)(.*)/
+      case arg
+      when /\A-(.)(.*)/
         if $1 == '-'
           arg, @maybe_arg = arg.split(/=/, 2)
           return arg
@@ -72,15 +73,15 @@ class ERB
             require ARGV.req_arg
           when '-S'                        # security level
             arg = ARGV.req_arg
-            raise "invalid safe_level #{arg.dump}" unless arg =~ /^[0-3]$/
+            raise "invalid safe_level #{arg.dump}" unless arg =~ /\A[0-3]\z/
             safe_level = arg.to_i
           when '-T'                        # trim mode
             arg = ARGV.req_arg
             if arg == '-'
               trim_mode = arg
               next
             end
-            raise "invalid trim mode #{arg.dump}" unless arg =~ /^[0-2]$/
+            raise "invalid trim mode #{arg.dump}" unless arg =~ /\A[0-2]\z/
             trim_mode = arg.to_i
           when '-E', '--encoding'
             arg = ARGV.req_arg