pg_basebackup: Fix progress messages when writing to a file

The progress messages print out \r to keep overwriting the same line on
the screen.  But this does not yield useful results when writing the
output to a file.  So in that case, print out \n instead.

Author: Martín Marqués <martin@2ndquadrant.com>
Reviewed-by: Arthur Zakirov <a.zakirov@postgrespro.ru>

src/bin/pg_basebackup/pg_basebackup.c

@@ -811,7 +811,10 @@ progress_report(int tablespacenum, const char *filename, bool force)
 				totaldone_str, totalsize_str, percent,
 				tablespacenum, tablespacecount);
 
-	fprintf(stderr, "\r");
+	if (isatty(fileno(stderr)))
+		fprintf(stderr, "\r");
+	else
+		fprintf(stderr, "\n");
 }
 
 static int32
@@ -1796,7 +1799,13 @@ BaseBackup(void)
 				progname);
 
 	if (showprogress && !verbose)
-		fprintf(stderr, "waiting for checkpoint\r");
+	{
+		fprintf(stderr, "waiting for checkpoint");
+		if (isatty(fileno(stderr)))
+			fprintf(stderr, "\r");
+		else
+			fprintf(stderr, "\n");
+	}
 
 	basebkp =
 		psprintf("BASE_BACKUP LABEL '%s' %s %s %s %s %s %s",
@@ -1929,7 +1938,8 @@ BaseBackup(void)
 	if (showprogress)
 	{
 		progress_report(PQntuples(res), NULL, true);
-		fprintf(stderr, "\n");	/* Need to move to next line */
+		if (isatty(fileno(stderr)))
+			fprintf(stderr, "\n");	/* Need to move to next line */
 	}
 
 	PQclear(res);