On Windows, use COMSPEC to find the location of cmd.exe.

Historically, psql consulted COMSPEC to spawn a shell in its \! command,
but we just invoked "cmd" when spawning shells in pg_ctl and pg_regress.
It seems better to rely on the environment variable, if it's set,
in all cases.

It's debatable whether this is a bug fix or just a behavioral change,
so no back-patch.

Juan José Santamaría Flecha

Discussion: https://postgr.es/m/16080-5d7f03222469f717@postgresql.org

src/bin/pg_ctl/pg_ctl.c

@@ -513,13 +513,19 @@ start_postmaster(void)
 	 * "exec", so we don't get to find out the postmaster's PID immediately.
 	 */
 	PROCESS_INFORMATION pi;
+	const char *comspec;
+
+	/* Find CMD.EXE location using COMSPEC, if it's set */
+	comspec = getenv("COMSPEC");
+	if (comspec == NULL)
+		comspec = "CMD";
 
 	if (log_file != NULL)
-		snprintf(cmd, MAXPGPATH, "CMD /C \"\"%s\" %s%s < \"%s\" >> \"%s\" 2>&1\"",
-				 exec_path, pgdata_opt, post_opts, DEVNULL, log_file);
+		snprintf(cmd, MAXPGPATH, "\"%s\" /C \"\"%s\" %s%s < \"%s\" >> \"%s\" 2>&1\"",
+				 comspec, exec_path, pgdata_opt, post_opts, DEVNULL, log_file);
 	else
-		snprintf(cmd, MAXPGPATH, "CMD /C \"\"%s\" %s%s < \"%s\" 2>&1\"",
-				 exec_path, pgdata_opt, post_opts, DEVNULL);
+		snprintf(cmd, MAXPGPATH, "\"%s\" /C \"\"%s\" %s%s < \"%s\" 2>&1\"",
+				 comspec, exec_path, pgdata_opt, post_opts, DEVNULL);
 
 	if (!CreateRestrictedProcess(cmd, &pi, false))
 	{

src/test/regress/pg_regress.c

@@ -1193,9 +1193,15 @@ spawn_process(const char *cmdline)
 	PROCESS_INFORMATION pi;
 	char	   *cmdline2;
 	HANDLE		restrictedToken;
+	const char *comspec;
+
+	/* Find CMD.EXE location using COMSPEC, if it's set */
+	comspec = getenv("COMSPEC");
+	if (comspec == NULL)
+		comspec = "CMD";
 
 	memset(&pi, 0, sizeof(pi));
-	cmdline2 = psprintf("cmd /c \"%s\"", cmdline);
+	cmdline2 = psprintf("\"%s\" /c \"%s\"", comspec, cmdline);
 
 	if ((restrictedToken =
 		 CreateRestrictedProcess(cmdline2, &pi)) == 0)