t/README: justify why "! grep foo" is sufficient

diff --git a/t/t4020-diff-external.sh b/t/t4020-diff-external.sh
index 2e7d73f0906e6a2808706236328470b2d855e9f9..8a309795c9c9654446d82c2e474e1ca08486e081 100755 (executable)
--- a/t/t4020-diff-external.sh
+++ b/t/t4020-diff-external.sh
@@ -177,7 +177,7 @@ test_expect_success 'no diff with -diff' '
        git diff | grep Binary
 '
 
-echo NULZbetweenZwords | "$PERL_PATH" -pe 'y/Z/\000/' > file
+echo NULZbetweenZwords | perl -pe 'y/Z/\000/' > file
 
 test_expect_success 'force diff with "diff"' '
        echo >.gitattributes "file diff" &&