Corrected with rubocop cop 'Style/RegexpLiteral'.

app/controllers/getting_started_controller.rb

@@ -76,7 +76,7 @@ curl http://localhost/api/v1/getting_started -v -u #{login}:#{password}
     # validate url
     messages = {}
     if !Setting.get('system_online_service')
-      if !params[:url] || params[:url] !~ /^(http|https):\/\/.+?$/
+      if !params[:url] || params[:url] !~ %r{^(http|https)://.+?$}
         messages[:url] = 'A URL looks like http://zammad.example.com'
       end
     end
@@ -107,7 +107,7 @@ curl http://localhost/api/v1/getting_started -v -u #{login}:#{password}
     # split url in http_type and fqdn
     settings = {}
     if !Setting.get('system_online_service')
-      if params[:url] =~ /^(http|https):\/\/(.+?)$/
+      if params[:url] =~ %r{/^(http|https)://(.+?)$}
         Setting.set('http_type', $1)
         settings[:http_type] = $1
         Setting.set('fqdn', $2)

app/controllers/import_otrs_controller.rb

@@ -6,7 +6,7 @@ class ImportOtrsController < ApplicationController
     return if setup_done_response
 
     # validate
-    if !params[:url] || params[:url] !~ /^(http|https):\/\/.+?$/
+    if !params[:url] || params[:url] !~ %r{^(http|https)://.+?$}
       render json: {
         result: 'invalid',
         message: 'Invalid!',
@@ -44,7 +44,7 @@ class ImportOtrsController < ApplicationController
     suffixes.each {|suffix|
       url = params[:url] + suffix + '?Action=ZammadMigrator'
       # strip multible / in url
-      url.gsub!(/([^:])(\/+\/)/, '\\1/')
+      url.gsub!(%r{([^:])(/+/)}, '\\1/')
       response = UserAgent.request( url )
 
       #Setting.set('import_mode', true)

app/models/avatar.rb

@@ -110,7 +110,7 @@ add a avatar
 
       # twitter workaround to get bigger avatar images
       # see also https://dev.twitter.com/overview/general/user-profile-images-and-banners
-      if data[:url] =~ /\/\/pbs.twimg.com\//i
+      if data[:url] =~ %r{//pbs.twimg.com/}i
         data[:url].sub!(/normal\.png$/, 'bigger.png')
       end
 

app/models/package.rb

@@ -82,7 +82,7 @@ class Package < ApplicationModel
   def self._package_base_dir?(package_base_dir)
     package = false
     Dir.glob(  package_base_dir + '/*.szpm') do |entry|
-      package = entry.sub( /^.*\/(.+?)\.szpm$/, '\1')
+      package = entry.sub( %r{^.*/(.+?)\.szpm$}, '\1')
     end
     if package == false
       raise "Can't link package, '#{package_base_dir}' is no package source directory!"
@@ -133,7 +133,7 @@ class Package < ApplicationModel
       entry = entry.sub( '//', '/' )
       file = entry
       file = file.sub( /#{package_base_dir.to_s}/, '' )
-      file = file.sub( /^\//, '' )
+      file = file.sub( %r{^/}, '' )
 
       # ignore files
       if file =~ /^README/

lib/core_ext/string.rb

@@ -83,10 +83,10 @@ class String
     string.gsub!( /^\s*/m, '' )
 
     # pre/code handling 1/2
-    string.gsub!( /<pre>(.+?)<\/pre>/m ) { |placeholder|
+    string.gsub!( %r{<pre>(.+?)</pre>}m ) { |placeholder|
       placeholder = placeholder.gsub(/\n/, '###BR###')
     }
-    string.gsub!( /<code>(.+?)<\/code>/m ) { |placeholder|
+    string.gsub!( %r{<code>(.+?)</code>/}m ) { |placeholder|
       placeholder = placeholder.gsub(/\n/, '###BR###')
     }
 
@@ -103,12 +103,12 @@ class String
     string.gsub!(/<blockquote(| [^>]*)>/i, '> ')
 
     # add hr
-    string.gsub!(/<hr(|\/| [^>]*)>/i, "___\n")
+    string.gsub!(%r{<hr(|/| [^>]*)>}i, "___\n")
 
     # add new lines
-    string.gsub!( /\<(br|table)(|\/| [^>]*)\>/i, "\n" )
+    string.gsub!( %r{\<(br|table)(|/| [^>]*)\>}i, "\n" )
-    string.gsub!( /\<\/(div|p|pre|blockquote|table|tr)(|\s.+?)\>/i, "\n" )
+    string.gsub!( %r{\</(div|p|pre|blockquote|table|tr)(|\s.+?)\>}i, "\n" )
-    string.gsub!( /\<\/td\>/i, ' '  )
+    string.gsub!( %r{/</td\>}i, ' '  )
 
     # strip all other tags
     string.gsub!( /\<.+?\>/, '' )