fix: IO::MultiWriter not add STDOUT twice

Author: initdc

README.md

@@ -10,7 +10,7 @@
    dependencies:
      exec:
        github: initdc/exec.cr
-       version: 0.2.0
+       version: 0.2.1
    ```
 
 2. Run `shards install`

shard.yml

@@ -1,5 +1,5 @@
 name: exec
-version: 0.2.0
+version: 0.2.1
 
 authors:
   - initdc <initd@outlook.com>

spec/exec_spec.cr

@@ -25,6 +25,10 @@ describe Exec do
     Exec.run("uname").should eq "Linux\n"
   end
 
+  it "print once Linux\n" do
+    Exec.run("uname", output: STDOUT).should eq "Linux\n"
+  end
+
   it "looks like ruby Open3 when bad" do
     r = Exec.run("echo good && echo bad >&2 && exit 1")
     case r

src/exec.cr

@@ -1,5 +1,5 @@
 class Exec < Process
-  VERSION = "0.2.0"
+  VERSION = "0.2.1"
 
   class IO
     class MultiWriter < ::IO::MultiWriter
@@ -19,20 +19,20 @@ class Exec < Process
     output_writer = if output.is_a?(Redirect)
                       output == Redirect::Close ? output : Exec::IO::MultiWriter.new(STDOUT, output_strio)
                     else
-                      Exec::IO::MultiWriter.new(STDOUT, output, output_strio)
+                      output != STDOUT ? Exec::IO::MultiWriter.new(STDOUT, output, output_strio) : Exec::IO::MultiWriter.new(STDOUT, output_strio)
                     end
 
     error_writer = if error.is_a?(Redirect)
                      error == Redirect::Close ? error : Exec::IO::MultiWriter.new(STDERR, error_strio)
                    else
-                     Exec::IO::MultiWriter.new(STDERR, error, error_strio)
+                     error != STDERR ? Exec::IO::MultiWriter.new(STDERR, error, error_strio) : Exec::IO::MultiWriter.new(STDERR, error_strio)
                    end
 
     status = new(command, args, env, clear_env, shell, input, output_writer, error_writer, chdir).wait
     $? = status
 
-    output.close unless output.is_a?(Redirect)
-    error.close unless error.is_a?(Redirect)
+    output.close unless output.is_a?(Redirect) || output == STDOUT
+    error.close unless error.is_a?(Redirect) || error == STDERR
     output_strio.close
     error_strio.close