[PATCH v4 6/6] tests: fix and add lint for non-portable grep --file

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

The --file option to grep isn't in POSIX[1], but -f is[1]. Let's check
for that in the future, and fix the portability regression in
f237c8b6fe ("commit-graph: implement git-commit-graph write",
2018-04-02) that broke e.g. AIX.

1. http://pubs.opengroup.org/onlinepubs/009695399/utilities/grep.html

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 t/check-non-portable-shell.pl | 1 +
 t/t5318-commit-graph.sh       | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/t/check-non-portable-shell.pl b/t/check-non-portable-shell.pl
index 75f38298d7..b45bdac688 100755
--- a/t/check-non-portable-shell.pl
+++ b/t/check-non-portable-shell.pl
@@ -43,6 +43,7 @@ sub err {
 	/\bwc -l.*"\s*=/ and err '`"$(wc -l)"` is not portable (use test_line_count)';
 	/\bhead\s+-c\b/ and err 'head -c is not portable (use test_copy_bytes BYTES <file >out)';
 	/(?:\$\(seq|^\s*seq\b)/ and err 'seq is not portable (use test_seq)';
+	/\bgrep\b.*--file\b/ and err 'grep --file FILE is not portable (use grep -f FILE)';
 	/\bexport\s+[A-Za-z0-9_]*=/ and err '"export FOO=bar" is not portable (use FOO=bar && export FOO)';
 	/^\s*([A-Z0-9_]+=(\w+|(["']).*?\3)\s+)+(\w+)/ and exists($func{$4}) and
 		err '"FOO=bar shell_func" assignment extends beyond "shell_func"';
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 3c1ffad491..0c500f7ca2 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -134,7 +134,7 @@ test_expect_success 'Add one more commit' '
 	git branch commits/8 &&
 	ls $objdir/pack | grep idx >existing-idx &&
 	git repack &&
-	ls $objdir/pack| grep idx | grep -v --file=existing-idx >new-idx
+	ls $objdir/pack| grep idx | grep -v -f existing-idx >new-idx
 '
 
 # Current graph structure:
-- 
2.18.0.865.gffc8e1a3cd6