support `-` as an argument to `rails runner`

in Rails 4.0, you could use `/dev/stdin` on both Linux and Mac, but with
the switch to Kernel.load in Rails 4.1, this broke on Linux (you get
a LoadError). Instead, explicitly detect `-` as meaning stdin, then
read from stdin explicitly, instead of performing file gymnastics. This
should now work on any platform uniformly.

Passing a script via stdin is useful when you're sshing to a server,
and the script you want to run is stored locally. You could theoretically
pass the entire script on the command line, but in reality you'll run
into problems with the command being too long.

4 files changed, 20 insertions, 2 deletions

diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index f720b7caab..45e1f5f3ea 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -1,3 +1,8 @@
+*   Support `-` as a platform-agnostic way to run a script from stdin with
+    `rails runner`
+
+    *Cody Cutrer*
+
 *   Add `bootsnap` to default `Gemfile`.
 
     *Burke Libbey*
diff --git a/railties/lib/rails/commands/runner/USAGE b/railties/lib/rails/commands/runner/USAGE
index b2a6e8493d..24b60037f0 100644
--- a/railties/lib/rails/commands/runner/USAGE
+++ b/railties/lib/rails/commands/runner/USAGE
@@ -8,6 +8,9 @@ Run the Ruby file located at `path/to/filename.rb` after loading the app:
 
   <%= executable %> path/to/filename.rb
 
+Run the Ruby script read from stdin after loading the app:
+  <%= executable %> -
+
 <% unless Gem.win_platform? %>
 You can also use the runner command as a shebang line for your executables:
 
diff --git a/railties/lib/rails/commands/runner/runner_command.rb b/railties/lib/rails/commands/runner/runner_command.rb
index 6864a9726b..c931fc2152 100644
--- a/railties/lib/rails/commands/runner/runner_command.rb
+++ b/railties/lib/rails/commands/runner/runner_command.rb
@@ -13,7 +13,7 @@ module Rails
       end
 
       def self.banner(*)
-        "#{super} [<'Some.ruby(code)'> | <filename.rb>]"
+        "#{super} [<'Some.ruby(code)'> | <filename.rb> | -]"
       end
 
       def perform(code_or_file = nil, *command_argv)
@@ -29,7 +29,9 @@ module Rails
 
         ARGV.replace(command_argv)
 
-        if File.exist?(code_or_file)
+        if code_or_file == "-"
+          eval($stdin.read, binding, "stdin")
+        elsif File.exist?(code_or_file)
           $0 = code_or_file
           Kernel.load code_or_file
         else
diff --git a/railties/test/application/runner_test.rb b/railties/test/application/runner_test.rb
index 0c45bc398a..81f717b2c3 100644
--- a/railties/test/application/runner_test.rb
+++ b/railties/test/application/runner_test.rb
@@ -84,6 +84,14 @@ module ApplicationTests
       assert_match %w( a b ).to_s, Dir.chdir(app_path) { `bin/rails runner "bin/program_name.rb" a b` }
     end
 
+    def test_should_run_stdin
+      app_file "bin/count_users.rb", <<-SCRIPT
+      puts User.count
+      SCRIPT
+
+      assert_match "42", Dir.chdir(app_path) { `cat bin/count_users.rb | bin/rails runner -` }
+    end
+
     def test_with_hook
       add_to_config <<-RUBY
         runner do |app|