[qr/connection authenticated: identity="$system_user" method=peer/]);
+# Success as the regular expression matches and \1 is replaced in the given
+# subexpression.
+reset_pg_ident($node, 'mypeermap', qq{/^$system_user(.*)\$}, 'test\1mapuser');
+test_role(
+ $node,
+ qq{testmapuser},
+ 'peer',
+ 0,
+ 'with regular expression in user name map with \1 replaced',
+ log_like =>
+ [qr/connection authenticated: identity="$system_user" method=peer/]);
+
+# Failure as the regular expression does not include a subexpression, but
+# the database user contains \1, requesting a replacement.
+reset_pg_ident($node, 'mypeermap', qq{/^$system_user\$}, '\1testmapuser');
+test_role(
+ $node,
+ qq{testmapuser},
+ 'peer', 2,
+ 'with regular expression in user name map with \1 not replaced',
+ log_like => [
+ qr/regular expression "\^$system_user\$" has no subexpressions as requested by backreference in "\\1testmapuser"/
+ ]);
+
# Concatenate system_user to system_user.
$regex_test_string = $system_user . $system_user;