diff --git a/mergetools/vimdiff b/mergetools/vimdiff
index 734d15a03b025e..f8ad6b35d4dbde 100644
--- a/mergetools/vimdiff
+++ b/mergetools/vimdiff
@@ -325,7 +325,7 @@ gen_cmd () {
 		fi
 
 		# If this is a single window diff with all the buffers
-		if ! echo "$tab" | grep ",\|/" >/dev/null
+		if ! echo "$tab" | grep -E ",|/" >/dev/null
 		then
 			CMD="$CMD | silent execute 'bufdo diffthis'"
 		fi
diff --git a/t/t0600-reffiles-backend.sh b/t/t0600-reffiles-backend.sh
index a390cffc800c62..92f570313d433a 100755
--- a/t/t0600-reffiles-backend.sh
+++ b/t/t0600-reffiles-backend.sh
@@ -424,7 +424,7 @@ test_expect_success SYMLINKS 'git branch -m with symlinked .git/refs' '
 	test_when_finished "rm -rf subdir" &&
 	git init --bare subdir &&
 
-	rm -rfv subdir/refs subdir/objects subdir/packed-refs &&
+	rm -rf subdir/refs subdir/objects subdir/packed-refs &&
 	ln -s ../.git/refs subdir/refs &&
 	ln -s ../.git/objects subdir/objects &&
 	ln -s ../.git/packed-refs subdir/packed-refs &&
diff --git a/t/t1404-update-ref-errors.sh b/t/t1404-update-ref-errors.sh
index 98e9158bd2ab41..67ebd81a4c7621 100755
--- a/t/t1404-update-ref-errors.sh
+++ b/t/t1404-update-ref-errors.sh
@@ -100,7 +100,7 @@ df_test() {
 		printf "%s\n" "delete $delname" "create $addname $D"
 	fi >commands &&
 	test_must_fail git update-ref --stdin <commands 2>output.err &&
-	grep "fatal:\( cannot lock ref $SQ$addname$SQ:\)\? $SQ$delref$SQ exists; cannot create $SQ$addref$SQ" output.err &&
+	grep -E "fatal:( cannot lock ref $SQ$addname$SQ:)? $SQ$delref$SQ exists; cannot create $SQ$addref$SQ" output.err &&
 	printf "%s\n" "$C $delref" >expected-refs &&
 	git for-each-ref --format="%(objectname) %(refname)" $prefix/r >actual-refs &&
 	test_cmp expected-refs actual-refs
diff --git a/t/t1700-split-index.sh b/t/t1700-split-index.sh
index a7b7263b35d1d8..ac4a5b2734c078 100755
--- a/t/t1700-split-index.sh
+++ b/t/t1700-split-index.sh
@@ -527,7 +527,7 @@ test_expect_success 'reading split index at alternate location' '
 
 	# ... and, for backwards compatibility, in the current GIT_DIR
 	# as well.
-	mv -v ./reading-alternate-location/.git/sharedindex.* .git &&
+	mv ./reading-alternate-location/.git/sharedindex.* .git &&
 	GIT_INDEX_FILE=./reading-alternate-location/.git/index \
 	git ls-files --cached >actual &&
 	test_cmp expect actual
diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index 60fe60d7610e2a..86c695eb0aef8d 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -2022,7 +2022,7 @@ test_expect_success GPGSM 'log --graph --show-signature x509' '
 test_expect_success GPGSSH 'log --graph --show-signature ssh' '
 	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
 	git log --graph --show-signature -n1 signed-ssh >actual &&
-	grep "${GOOD_SIGNATURE_TRUSTED}" actual
+	grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
 '
 
 test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'log shows failure on expired signature key' '
diff --git a/t/t9001-send-email.sh b/t/t9001-send-email.sh
index 5a771000c9ca0d..58699f8e4eedd6 100755
--- a/t/t9001-send-email.sh
+++ b/t/t9001-send-email.sh
@@ -2526,7 +2526,7 @@ test_expect_success $PREREQ 'test forbidSendmailVariables behavior override' '
 
 test_expect_success $PREREQ '--compose handles lowercase headers' '
 	write_script fake-editor <<-\EOF &&
-	sed "s/^From:.*/from: edited-from@example.com/i" "$1" >"$1.tmp" &&
+	sed "s/^[Ff][Rr][Oo][Mm]:.*/from: edited-from@example.com/" "$1" >"$1.tmp" &&
 	mv "$1.tmp" "$1"
 	EOF
 	clean_fake_sendmail &&
diff --git a/t/t9118-git-svn-funky-branch-names.sh b/t/t9118-git-svn-funky-branch-names.sh
index d3261e35b81840..a34fd46ecc5a39 100755
--- a/t/t9118-git-svn-funky-branch-names.sh
+++ b/t/t9118-git-svn-funky-branch-names.sh
@@ -38,7 +38,7 @@ test_expect_success 'setup svnrepo' '
 # SVN 1.7 will truncate "not-a%40{0]" to just "not-a".
 # Look at what SVN wound up naming the branch and use that.
 # Be sure to escape the @ if it shows up.
-non_reflog=$(svn_cmd ls "$svnrepo/pr ject/branches" | sed -ne '/not-a/ { s/\///; s/@/%40/; p }')
+non_reflog=$(svn_cmd ls "$svnrepo/pr ject/branches" | sed -ne '/not-a/ { s/\///; s/@/%40/; p; }')
 
 test_expect_success 'test clone with funky branch names' '
 	git svn clone -s "$svnrepo/pr ject" project &&
diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
index 963f865f27ed05..ed3d03367ec6c2 100755
--- a/t/t9902-completion.sh
+++ b/t/t9902-completion.sh
@@ -73,7 +73,7 @@ _get_comp_words_by_ref ()
 print_comp ()
 {
 	local IFS=$'\n'
-	echo "${COMPREPLY[*]}" > out
+	printf '%s\n' "${COMPREPLY[*]}" > out
 }
 
 run_completion ()