Switch pg_regress to output unified diffs by default

Author: Christoph Berg <myon@debian.org>
Discussion: https://www.postgresql.org/message-id/flat/20170406223103.ixihdedf6d6d4kbk@alap3.anarazel.de/

Author: petere

doc/src/sgml/regress.sgml

@@ -410,7 +410,7 @@ make standbycheck
     If you don't
     like the <command>diff</command> options that are used by default, set the
     environment variable <envar>PG_REGRESS_DIFF_OPTS</envar>, for
-    instance <literal>PG_REGRESS_DIFF_OPTS='-u'</literal>.  (Or you
+    instance <literal>PG_REGRESS_DIFF_OPTS='-c'</literal>.  (Or you
     can run <command>diff</command> yourself, if you prefer.)
    </para>
 

src/test/regress/pg_regress.c

@@ -62,10 +62,10 @@ static char *shellprog = SHELLPROG;
  */
 #ifndef WIN32
 const char *basic_diff_opts = "";
-const char *pretty_diff_opts = "-C3";
+const char *pretty_diff_opts = "-U3";
 #else
 const char *basic_diff_opts = "-w";
-const char *pretty_diff_opts = "-w -C3";
+const char *pretty_diff_opts = "-w -U3";
 #endif
 
 /* options settable from command line */