Fix in-place editing to use atomic file operations

mrblib/rf/runner.rb

@@ -51,7 +51,6 @@ def run
         if in_place
           write_file = write_open(filename, in_place)
           $output = write_file
-          tempfile = write_file if in_place.empty?
         end
 
         records = filter.new(input)
@@ -60,11 +59,11 @@ def run
         binary_match = apply_expressions(records)
         warn_binary_match(filename) if binary_match
 
-        next unless tempfile
+        next if $output == $stdout
 
-        tempfile.close
+        $output.close
         input.close
-        File.rename(tempfile.path, filename)
+        File.rename($output.path, filename)
       end
     end
 
@@ -83,15 +82,17 @@ def read_open(file)
     end
 
     def write_open(file, in_place)
-      if in_place.empty?
-        dir = File.dirname(file)
-        Tempfile.new('.rf', dir)
-      else
-        raise NotFound, file unless File.exist?(file)
-        raise NotRegularFile, file unless File.file?(file)
+      raise NotFound, file unless File.exist?(file)
+      raise NotRegularFile, file unless File.file?(file)
 
-        File.open("#{file}#{in_place}", 'w')
+      if in_place
+        File.open("#{file}#{in_place}", 'w') do |f| # rubocop: disable Style/FileWrite
+          f.write(File.read(file))
+        end
       end
+
+      dir = File.dirname(file)
+      Tempfile.new('.rf', dir)
     end
 
     def split(val)

spec/global_options/in_place_option_spec.rb

@@ -19,9 +19,13 @@
     end
 
     it_behaves_like 'a successful exec' do
-      let(:file_content) { read_file("foo#{suffix}") }
+      let(:file_content) { read_file('foo') }
 
       it { expect(file_content).to eq "bar\n" }
+
+      it 'creates backup file when suffix is provided' do
+        expect(read_file("foo#{suffix}")).to eq 'foo' unless suffix.empty?
+      end
     end
   end