diff --git a/lib/jekyll/commands/doctor.rb b/lib/jekyll/commands/doctor.rb
index 8ce2c473..a29cbf7e 100644
--- a/lib/jekyll/commands/doctor.rb
+++ b/lib/jekyll/commands/doctor.rb
@@ -39,8 +39,8 @@ module Jekyll
 
         def deprecated_relative_permalinks(site)
           if site.config['relative_permalinks']
-            Jekyll::Deprecator.deprecation_message "Your site still uses relative" +
-                                " permalinks, which was removed in" +
+            Jekyll::Deprecator.deprecation_message "Your site still uses relative" \
+                                " permalinks, which was removed in" \
                                 " Jekyll v3.0.0."
             return true
           end
@@ -54,7 +54,7 @@ module Jekyll
           urls.each do |url, paths|
             if paths.size > 1
               conflicting_urls = true
-              Jekyll.logger.warn "Conflict:", "The URL '#{url}' is the destination" +
+              Jekyll.logger.warn "Conflict:", "The URL '#{url}' is the destination" \
                 " for the following pages: #{paths.join(", ")}"
             end
           end
@@ -83,8 +83,8 @@ module Jekyll
           urls.each do |case_insensitive_url, real_urls|
             if real_urls.uniq.size > 1
               urls_only_differ_by_case = true
-              Jekyll.logger.warn "Warning:", "The following URLs only differ" +
-                " by case. On a case-insensitive file system one of the URLs" +
+              Jekyll.logger.warn "Warning:", "The following URLs only differ" \
+                " by case. On a case-insensitive file system one of the URLs" \
                 " will be overwritten by the other: #{real_urls.join(", ")}"
             end
           end
diff --git a/lib/jekyll/configuration.rb b/lib/jekyll/configuration.rb
index e01f798c..21929f3f 100644
--- a/lib/jekyll/configuration.rb
+++ b/lib/jekyll/configuration.rb
@@ -173,7 +173,7 @@ module Jekyll
           configuration = Utils.deep_merge_hashes(configuration, new_config)
         end
       rescue ArgumentError => err
-        Jekyll.logger.warn "WARNING:", "Error reading configuration. " +
+        Jekyll.logger.warn "WARNING:", "Error reading configuration. " \
                      "Using defaults (and options)."
         $stderr.puts "#{err}"
       end
@@ -198,16 +198,16 @@ module Jekyll
       config = clone
       # Provide backwards-compatibility
       if config.key?('auto') || config.key?('watch')
-        Jekyll::Deprecator.deprecation_message "Auto-regeneration can no longer" +
-                            " be set from your configuration file(s). Use the"+
+        Jekyll::Deprecator.deprecation_message "Auto-regeneration can no longer" \
+                            " be set from your configuration file(s). Use the"\
                             " --[no-]watch/-w command-line option instead."
         config.delete('auto')
         config.delete('watch')
       end
 
       if config.key? 'server'
-        Jekyll::Deprecator.deprecation_message "The 'server' configuration option" +
-                            " is no longer accepted. Use the 'jekyll serve'" +
+        Jekyll::Deprecator.deprecation_message "The 'server' configuration option" \
+                            " is no longer accepted. Use the 'jekyll serve'" \
                             " subcommand to serve your site with WEBrick."
         config.delete('server')
       end
@@ -218,9 +218,9 @@ module Jekyll
       renamed_key 'data_source', 'data_dir', config
 
       if config.key? 'pygments'
-        Jekyll::Deprecator.deprecation_message "The 'pygments' configuration option" +
-                            " has been renamed to 'highlighter'. Please update your" +
-                            " config file accordingly. The allowed values are 'rouge', " +
+        Jekyll::Deprecator.deprecation_message "The 'pygments' configuration option" \
+                            " has been renamed to 'highlighter'. Please update your" \
+                            " config file accordingly. The allowed values are 'rouge', " \
                             "'pygments' or null."
 
         config['highlighter'] = 'pygments' if config['pygments']
@@ -230,9 +230,9 @@ module Jekyll
       %w[include exclude].each do |option|
         config[option] ||= []
         if config[option].is_a?(String)
-          Jekyll::Deprecator.deprecation_message "The '#{option}' configuration option" +
-            " must now be specified as an array, but you specified" +
-            " a string. For now, we've treated the string you provided" +
+          Jekyll::Deprecator.deprecation_message "The '#{option}' configuration option" \
+            " must now be specified as an array, but you specified" \
+            " a string. For now, we've treated the string you provided" \
             " as a list of comma-separated values."
           config[option] = csv_to_array(config[option])
         end
@@ -240,16 +240,16 @@ module Jekyll
       end
 
       if (config['kramdown'] || {}).key?('use_coderay')
-        Jekyll::Deprecator.deprecation_message "Please change 'use_coderay'" +
+        Jekyll::Deprecator.deprecation_message "Please change 'use_coderay'" \
           " to 'enable_coderay' in your configuration file."
         config['kramdown']['use_coderay'] = config['kramdown'].delete('enable_coderay')
       end
 
       if config.fetch('markdown', 'kramdown').to_s.downcase.eql?("maruku")
-        Jekyll.logger.abort_with "Error:", "You're using the 'maruku' " +
-          "Markdown processor, which has been removed as of 3.0.0. " +
-          "We recommend you switch to Kramdown. To do this, replace " +
-          "`markdown: maruku` with `markdown: kramdown` in your " +
+        Jekyll.logger.abort_with "Error:", "You're using the 'maruku' " \
+          "Markdown processor, which has been removed as of 3.0.0. " \
+          "We recommend you switch to Kramdown. To do this, replace " \
+          "`markdown: maruku` with `markdown: kramdown` in your " \
           "`_config.yml` file."
       end
 
@@ -260,7 +260,7 @@ module Jekyll
       config = clone
 
       if config.key?('paginate') && (!config['paginate'].is_a?(Integer) || config['paginate'] < 1)
-        Jekyll.logger.warn "Config Warning:", "The `paginate` key must be a" +
+        Jekyll.logger.warn "Config Warning:", "The `paginate` key must be a" \
           " positive integer or nil. It's currently set to '#{config['paginate'].inspect}'."
         config['paginate'] = nil
       end
@@ -285,8 +285,8 @@ module Jekyll
 
     def renamed_key(old, new, config, allowed_values = nil)
       if config.key?(old)
-        Jekyll::Deprecator.deprecation_message "The '#{old}' configuration" +
-          "option has been renamed to '#{new}'. Please update your config " +
+        Jekyll::Deprecator.deprecation_message "The '#{old}' configuration" \
+          "option has been renamed to '#{new}'. Please update your config " \
           "file accordingly."
         config[new] = config.delete(old)
       end
diff --git a/lib/jekyll/filters.rb b/lib/jekyll/filters.rb
index 2b1bf1af..2ba0fac3 100644
--- a/lib/jekyll/filters.rb
+++ b/lib/jekyll/filters.rb
@@ -234,7 +234,7 @@ module Jekyll
         when nils == "last"
           order = + 1
         else
-          raise ArgumentError.new("Invalid nils order: " +
+          raise ArgumentError.new("Invalid nils order: " \
             "'#{nils}' is not a valid nils order. It must be 'first' or 'last'.")
         end
 
diff --git a/lib/jekyll/hooks.rb b/lib/jekyll/hooks.rb
index a9a5e735..74c01bbb 100644
--- a/lib/jekyll/hooks.rb
+++ b/lib/jekyll/hooks.rb
@@ -67,7 +67,7 @@ module Jekyll
       }
 
       unless @registry[owner][event]
-        raise NotAvailable, "Invalid hook. #{owner} supports only the " <<
+        raise NotAvailable, "Invalid hook. #{owner} supports only the " \
           "following hooks #{@registry[owner].keys.inspect}"
       end
 
diff --git a/lib/jekyll/plugin_manager.rb b/lib/jekyll/plugin_manager.rb
index 11db89d1..da7bf121 100644
--- a/lib/jekyll/plugin_manager.rb
+++ b/lib/jekyll/plugin_manager.rb
@@ -86,8 +86,8 @@ module Jekyll
     def deprecation_checks
       pagination_included = (site.config['gems'] || []).include?('jekyll-paginate') || defined?(Jekyll::Paginate)
       if site.config['paginate'] && !pagination_included
-        Jekyll::Deprecator.deprecation_message "You appear to have pagination " +
-          "turned on, but you haven't included the `jekyll-paginate` gem. " +
+        Jekyll::Deprecator.deprecation_message "You appear to have pagination " \
+          "turned on, but you haven't included the `jekyll-paginate` gem. " \
           "Ensure you have `gems: [jekyll-paginate]` in your configuration file."
       end
     end
diff --git a/lib/jekyll/site.rb b/lib/jekyll/site.rb
index 4dc3ac84..2575eba2 100644
--- a/lib/jekyll/site.rb
+++ b/lib/jekyll/site.rb
@@ -292,10 +292,10 @@ module Jekyll
     # Returns
     def relative_permalinks_are_deprecated
       if config['relative_permalinks']
-        Jekyll.logger.abort_with "Since v3.0, permalinks for pages" +
-                                " in subfolders must be relative to the" +
-                                " site source directory, not the parent" +
-                                " directory. Check http://jekyllrb.com/docs/upgrading/"+
+        Jekyll.logger.abort_with "Since v3.0, permalinks for pages" \
+                                " in subfolders must be relative to the" \
+                                " site source directory, not the parent" \
+                                " directory. Check http://jekyllrb.com/docs/upgrading/"\
                                 " for more info."
       end
     end
diff --git a/lib/jekyll/tags/highlight.rb b/lib/jekyll/tags/highlight.rb
index 3e64bc8b..616dfdbf 100644
--- a/lib/jekyll/tags/highlight.rb
+++ b/lib/jekyll/tags/highlight.rb
@@ -88,7 +88,7 @@ eos
           puts
           Jekyll.logger.error code
           puts
-          Jekyll.logger.error "While attempting to convert the above code, Pygments.rb" +
+          Jekyll.logger.error "While attempting to convert the above code, Pygments.rb" \
             " returned an unacceptable value."
           Jekyll.logger.error "This is usually a timeout problem solved by running `jekyll build` again."
           raise ArgumentError.new("Pygments.rb returned an unacceptable value when attempting to highlight some code.")
diff --git a/lib/jekyll/tags/post_url.rb b/lib/jekyll/tags/post_url.rb
index 5b0d6479..2da26ec0 100644
--- a/lib/jekyll/tags/post_url.rb
+++ b/lib/jekyll/tags/post_url.rb
@@ -70,9 +70,9 @@ eos
 
         site.posts.docs.each do |p|
           if @post.deprecated_equality p
-            Jekyll::Deprecator.deprecation_message "A call to '{{ post_url #{@post.name} }}' did not match " +
-              "a post using the new matching method of checking name " +
-              "(path-date-slug) equality. Please make sure that you " +
+            Jekyll::Deprecator.deprecation_message "A call to '{{ post_url #{@post.name} }}' did not match " \
+              "a post using the new matching method of checking name " \
+              "(path-date-slug) equality. Please make sure that you " \
               "change this tag to match the post's name exactly."
             return p.url
           end