text: #include "cache.h"
  #include "config.h"
  #include "strbuf.h"
  #include "run-command.h"
  #include "sigchain.h"
  
  #ifndef DEFAULT_EDITOR
  #define DEFAULT_EDITOR "vi"
  #endif
  
  int is_terminal_dumb(void)
  {
  	const char *terminal = getenv("TERM");
  	return !terminal || !strcmp(terminal, "dumb");
  }
  
  const char *git_editor(void)
  {
  	const char *editor = getenv("GIT_EDITOR");
  	int terminal_is_dumb = is_terminal_dumb();
  
  	if (!editor && editor_program)
  		editor = editor_program;
  	if (!editor && !terminal_is_dumb)
  		editor = getenv("VISUAL");
  	if (!editor)
  		editor = getenv("EDITOR");
  
  	if (!editor && terminal_is_dumb)
  		return NULL;
  
  	if (!editor)
  		editor = DEFAULT_EDITOR;
  
  	return editor;
  }
  
  const char *git_sequence_editor(void)
  {
  	const char *editor = getenv("GIT_SEQUENCE_EDITOR");
  
  	if (!editor)
  		git_config_get_string_tmp("sequence.editor", &editor);
  	if (!editor)
  		editor = git_editor();
  
  	return editor;
  }
  
  static int launch_specified_editor(const char *editor, const char *path,
  				   struct strbuf *buffer, const char *const *env)
  {
  	if (!editor)
  		return error("Terminal is dumb, but EDITOR unset");
  
  	if (strcmp(editor, ":")) {
  		struct strbuf realpath = STRBUF_INIT;
  		const char *args[] = { editor, NULL, NULL };
  		struct child_process p = CHILD_PROCESS_INIT;
  		int ret, sig;
  		int print_waiting_for_editor = advice_waiting_for_editor && isatty(2);
  
  		if (print_waiting_for_editor) {
  			/*
  			 * A dumb terminal cannot erase the line later on. Add a
  			 * newline to separate the hint from subsequent output.
  			 *
  			 * Make sure that our message is separated with a whitespace
  			 * from further cruft that may be written by the editor.
  			 */
  			const char term = is_terminal_dumb() ? '\n' : ' ';
  
  			fprintf(stderr,
  				_("hint: Waiting for your editor to close the file...%c"),
  				term);
  			fflush(stderr);
  		}
  
  		strbuf_realpath(&realpath, path, 1);
  		args[1] = realpath.buf;
  
  		p.argv = args;
  		p.env = env;
  		p.use_shell = 1;
  		p.trace2_child_class = "editor";
  		if (start_command(&p) < 0) {
  			strbuf_release(&realpath);
  			return error("unable to start editor '%s'", editor);
  		}
  
  		sigchain_push(SIGINT, SIG_IGN);
  		sigchain_push(SIGQUIT, SIG_IGN);
  		ret = finish_command(&p);
  		strbuf_release(&realpath);
  		sig = ret - 128;
  		sigchain_pop(SIGINT);
  		sigchain_pop(SIGQUIT);
  		if (sig == SIGINT || sig == SIGQUIT)
  			raise(sig);
  		if (ret)
  			return error("There was a problem with the editor '%s'.",
  					editor);
  
  		if (print_waiting_for_editor && !is_terminal_dumb())
  			/*
  			 * Erase the entire line to avoid wasting the
  			 * vertical space.
  			 */
  			term_clear_line();
  	}
  
  	if (!buffer)
  		return 0;
  	if (strbuf_read_file(buffer, path, 0) < 0)
  		return error_errno("could not read file '%s'", path);
  	return 0;
  }
  
  int launch_editor(const char *path, struct strbuf *buffer, const char *const *env)
  {
  	return launch_specified_editor(git_editor(), path, buffer, env);
  }
  
  int launch_sequence_editor(const char *path, struct strbuf *buffer,
  			   const char *const *env)
  {
  	return launch_specified_editor(git_sequence_editor(), path, buffer, env);
  }
  