t4019 "grep" portability fix

Input to "grep" is supposed to be "text", but we deliberately feed output
from "git diff --color" to sift it into two sets of lines (ones with
errors, the other without).  Some implementations of "grep" only report
matches with the exit status, without showing the matched lines in their
output (e.g. OpenBSD 4.6, which says "Binary file .. matches").

Fortunately, "grep -a" is often a way to force the command to treat its
input as text.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4019-diff-wserror.sh

@@ -20,11 +20,27 @@ test_expect_success setup '
 
 blue_grep='7;34m' ;# ESC [ 7 ; 3 4 m
 
+printf "\033[%s" "$blue_grep" >check-grep
+if (grep "$blue_grep" <check-grep | grep "$blue_grep") >/dev/null 2>&1
+then
+	grep_a=grep
+elif (grep -a "$blue_grep" <check-grep | grep -a "$blue_grep") >/dev/null 2>&1
+then
+	grep_a='grep -a'
+else
+	grep_a=grep ;# expected to fail...
+fi
+rm -f check-grep
+
+prepare_output () {
+	git diff --color >output
+	$grep_a "$blue_grep" output >error
+	$grep_a -v "$blue_grep" output >normal
+}
+
 test_expect_success default '
 
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT error >/dev/null &&
@@ -37,9 +53,7 @@ test_expect_success default '
 test_expect_success 'without -trail' '
 
 	git config core.whitespace -trail
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT error >/dev/null &&
@@ -53,9 +67,7 @@ test_expect_success 'without -trail (attribute)' '
 
 	git config --unset core.whitespace
 	echo "F whitespace=-trail" >.gitattributes
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT error >/dev/null &&
@@ -69,9 +81,7 @@ test_expect_success 'without -space' '
 
 	rm -f .gitattributes
 	git config core.whitespace -space
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT normal >/dev/null &&
@@ -85,9 +95,7 @@ test_expect_success 'without -space (attribute)' '
 
 	git config --unset core.whitespace
 	echo "F whitespace=-space" >.gitattributes
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT normal >/dev/null &&
@@ -101,9 +109,7 @@ test_expect_success 'with indent-non-tab only' '
 
 	rm -f .gitattributes
 	git config core.whitespace indent,-trailing,-space
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight error >/dev/null &&
 	grep HT normal >/dev/null &&
@@ -117,9 +123,7 @@ test_expect_success 'with indent-non-tab only (attribute)' '
 
 	git config --unset core.whitespace
 	echo "F whitespace=indent,-trailing,-space" >.gitattributes
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight error >/dev/null &&
 	grep HT normal >/dev/null &&
@@ -133,9 +137,7 @@ test_expect_success 'with cr-at-eol' '
 
 	rm -f .gitattributes
 	git config core.whitespace cr-at-eol
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT error >/dev/null &&
@@ -149,9 +151,7 @@ test_expect_success 'with cr-at-eol (attribute)' '
 
 	git config --unset core.whitespace
 	echo "F whitespace=trailing,cr-at-eol" >.gitattributes
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT error >/dev/null &&
@@ -195,7 +195,7 @@ test_expect_success 'color new trailing blank lines' '
 	git add x &&
 	{ echo a; echo; echo; echo; echo c; echo; echo; echo; echo; } >x &&
 	git diff --color x >output &&
-	cnt=$(grep "${blue_grep}" output | wc -l) &&
+	cnt=$($grep_a "${blue_grep}" output | wc -l) &&
 	test $cnt = 2
 '