diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
index 017f55adf4..9fd09dbe93 100755
--- a/t/t7800-difftool.sh
+++ b/t/t7800-difftool.sh
@@ -23,16 +23,6 @@ prompt_given ()
 	test "$prompt" = "Launch 'test-tool' [Y/n]: branch"
 }
 
-stdin_contains ()
-{
-	grep >/dev/null "$1"
-}
-
-stdin_doesnot_contain ()
-{
-	! stdin_contains "$1"
-}
-
 # Create a file on master and change it on branch
 test_expect_success PERL 'setup' '
 	echo master >file &&
@@ -296,24 +286,24 @@ test_expect_success PERL 'setup with 2 files different' '
 test_expect_success PERL 'say no to the first file' '
 	(echo n && echo) >input &&
 	git difftool -x cat branch <input >output &&
-	stdin_contains m2 <output &&
-	stdin_contains br2 <output &&
-	stdin_doesnot_contain master <output &&
-	stdin_doesnot_contain branch <output
+	grep m2 output &&
+	grep br2 output &&
+	! grep master output &&
+	! grep branch output
 '
 
 test_expect_success PERL 'say no to the second file' '
 	(echo && echo n) >input &&
 	git difftool -x cat branch <input >output &&
-	stdin_contains master <output &&
-	stdin_contains branch  <output &&
-	stdin_doesnot_contain m2 <output &&
-	stdin_doesnot_contain br2 <output
+	grep master output &&
+	grep branch output &&
+	! grep m2 output &&
+	! grep br2 output
 '
 
 test_expect_success PERL 'difftool --tool-help' '
 	git difftool --tool-help >output &&
-	stdin_contains tool <output
+	grep tool output
 '
 
 test_expect_success PERL 'setup change in subdirectory' '
@@ -330,28 +320,28 @@ test_expect_success PERL 'setup change in subdirectory' '
 
 test_expect_success PERL 'difftool -d' '
 	git difftool -d --extcmd ls branch >output &&
-	stdin_contains sub <output &&
-	stdin_contains file <output
+	grep sub output &&
+	grep file output
 '
 
 test_expect_success PERL 'difftool --dir-diff' '
 	git difftool --dir-diff --extcmd ls branch >output &&
-	stdin_contains sub <output &&
-	stdin_contains file <output
+	grep sub output &&
+	grep file output
 '
 
 test_expect_success PERL 'difftool --dir-diff ignores --prompt' '
 	git difftool --dir-diff --prompt --extcmd ls branch >output &&
-	stdin_contains sub <output &&
-	stdin_contains file <output
+	grep sub output &&
+	grep file output
 '
 
 test_expect_success PERL 'difftool --dir-diff from subdirectory' '
 	(
 		cd sub &&
 		git difftool --dir-diff --extcmd ls branch >output &&
-		stdin_contains sub <output &&
-		stdin_contains file <output
+		grep sub output &&
+		grep file output
 	)
 '