Improve Process tests and documents

io.c

@@ -533,10 +533,12 @@ static rb_io_t *flush_before_seek(rb_io_t *fptr);
 
 extern ID ruby_static_id_signo;
 
-NORETURN(static void raise_on_write(rb_io_t *fptr, int e, VALUE errinfo));
+NORETURN(static void rb_sys_fail_on_write(rb_io_t *fptr));
 static void
-raise_on_write(rb_io_t *fptr, int e, VALUE errinfo)
+rb_sys_fail_on_write(rb_io_t *fptr)
 {
+    int e = errno;
+    VALUE errinfo = rb_syserr_new_path(e, (fptr)->pathv);
 #if defined EPIPE
     if (fptr_signal_on_epipe(fptr) && (e == EPIPE)) {
         const VALUE sig =
@@ -550,12 +552,6 @@ raise_on_write(rb_io_t *fptr, int e, VALUE errinfo)
     rb_exc_raise(errinfo);
 }
 
-#define rb_sys_fail_on_write(fptr) \
-    do { \
-        int e = errno; \
-        raise_on_write(fptr, e, rb_syserr_new_path(e, (fptr)->pathv)); \
-    } while (0)
-
 #define NEED_NEWLINE_DECORATOR_ON_READ(fptr) ((fptr)->mode & FMODE_TEXTMODE)
 #define NEED_NEWLINE_DECORATOR_ON_WRITE(fptr) ((fptr)->mode & FMODE_TEXTMODE)
 #if defined(RUBY_TEST_CRLF_ENVIRONMENT) || defined(_WIN32)

process.c

@@ -8865,7 +8865,7 @@ proc_warmup(VALUE _)
  *
  * Argument +exe_path+ is one of the following:
  *
- * - The string path to an executable to be called:
+ * - The string path to an executable file to be called:
  *
  *   Example:
  *
@@ -8881,6 +8881,19 @@ proc_warmup(VALUE _)
  *   escape the entire command name using a shell in platform
  *   dependent manner, or use the array form below.
  *
+ *   If +exe_path+ does not contain any path separator, an executable
+ *   file is searched from directories specified with the +PATH+
+ *   environment variable.  What the word "executable" means here is
+ *   depending on platforms.
+ *
+ *   Even if the file considered "executable", its content may not be
+ *   in proper executable format.  In that case, Ruby tries to run it
+ *   by using <tt>/bin/sh</tt> on a Unix-like system, like system(3)
+ *   does.
+ *
+ *     File.write('shell_command', 'echo $SHELL', perm: 0o755)
+ *     system('./shell_command')        # prints "/bin/sh" or something.
+ *
  * - A 2-element array containing the path to an executable
  *   and the string to be used as the name of the executing process:
  *

spec/ruby/core/kernel/system_spec.rb

@@ -64,6 +64,23 @@
     end
   end
 
+  platform_is_not :windows do
+    before :each do
+      require 'tmpdir'
+      @shell_command = File.join(Dir.mktmpdir, "noshebang.cmd")
+      File.write(@shell_command, %[echo "$PATH"\n], perm: 0o700)
+    end
+
+    after :each do
+      File.unlink(@shell_command)
+      Dir.rmdir(File.dirname(@shell_command))
+    end
+
+    it "executes with `sh` if the command is executable but not binary and there is no shebang" do
+      -> { @object.system(@shell_command) }.should output_to_fd(ENV['PATH'] + "\n")
+    end
+  end
+
   before :each do
     ENV['TEST_SH_EXPANSION'] = 'foo'
     @shell_var = '$TEST_SH_EXPANSION'