selftests: mptcp: join: use += operator to append strings

This patch uses addition assignment operator (+=) to append strings instead
of open-coding in mptcp_join.sh. This can make the statements shorter.

Signed-off-by: Geliang Tang <[email protected]>

tools/testing/selftests/net/mptcp/mptcp_join.sh

@@ -755,18 +755,18 @@ pm_nl_check_endpoint()
 		line="${line% }"
 		# the dump order is: address id flags port dev
 		[ -n "$addr" ] && expected_line="$addr"
-		expected_line="$expected_line $id"
-		[ -n "$_flags" ] && expected_line="$expected_line ${_flags//","/" "}"
-		[ -n "$dev" ] && expected_line="$expected_line $dev"
-		[ -n "$port" ] && expected_line="$expected_line $port"
+		expected_line+=" $id"
+		[ -n "$_flags" ] && expected_line+=" ${_flags//","/" "}"
+		[ -n "$dev" ] && expected_line+=" $dev"
+		[ -n "$port" ] && expected_line+=" $port"
 	else
 		line=$(ip netns exec $ns ./pm_nl_ctl get $_id)
 		# the dump order is: id flags dev address port
 		expected_line="$id"
-		[ -n "$flags" ] && expected_line="$expected_line $flags"
-		[ -n "$dev" ] && expected_line="$expected_line $dev"
-		[ -n "$addr" ] && expected_line="$expected_line $addr"
-		[ -n "$_port" ] && expected_line="$expected_line $_port"
+		[ -n "$flags" ] && expected_line+=" $flags"
+		[ -n "$dev" ] && expected_line+=" $dev"
+		[ -n "$addr" ] && expected_line+=" $addr"
+		[ -n "$_port" ] && expected_line+=" $_port"
 	fi
 	if [ "$line" = "$expected_line" ]; then
 		print_ok
@@ -1217,7 +1217,7 @@ chk_csum_nr()
 	print_check "sum"
 	count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtDataCsumErr")
 	if [ "$count" != "$csum_ns1" ]; then
-		extra_msg="$extra_msg ns1=$count"
+		extra_msg+=" ns1=$count"
 	fi
 	if [ -z "$count" ]; then
 		print_skip
@@ -1230,7 +1230,7 @@ chk_csum_nr()
 	print_check "csum"
 	count=$(mptcp_lib_get_counter ${ns2} "MPTcpExtDataCsumErr")
 	if [ "$count" != "$csum_ns2" ]; then
-		extra_msg="$extra_msg ns2=$count"
+		extra_msg+=" ns2=$count"
 	fi
 	if [ -z "$count" ]; then
 		print_skip
@@ -1274,7 +1274,7 @@ chk_fail_nr()
 	print_check "ftx"
 	count=$(mptcp_lib_get_counter ${ns_tx} "MPTcpExtMPFailTx")
 	if [ "$count" != "$fail_tx" ]; then
-		extra_msg="$extra_msg,tx=$count"
+		extra_msg+=",tx=$count"
 	fi
 	if [ -z "$count" ]; then
 		print_skip
@@ -1288,7 +1288,7 @@ chk_fail_nr()
 	print_check "failrx"
 	count=$(mptcp_lib_get_counter ${ns_rx} "MPTcpExtMPFailRx")
 	if [ "$count" != "$fail_rx" ]; then
-		extra_msg="$extra_msg,rx=$count"
+		extra_msg+=",rx=$count"
 	fi
 	if [ -z "$count" ]; then
 		print_skip
@@ -1323,7 +1323,7 @@ chk_fclose_nr()
 	if [ -z "$count" ]; then
 		print_skip
 	elif [ "$count" != "$fclose_tx" ]; then
-		extra_msg="$extra_msg,tx=$count"
+		extra_msg+=",tx=$count"
 		fail_test "got $count MP_FASTCLOSE[s] TX expected $fclose_tx"
 	else
 		print_ok
@@ -1334,7 +1334,7 @@ chk_fclose_nr()
 	if [ -z "$count" ]; then
 		print_skip
 	elif [ "$count" != "$fclose_rx" ]; then
-		extra_msg="$extra_msg,rx=$count"
+		extra_msg+=",rx=$count"
 		fail_test "got $count MP_FASTCLOSE[s] RX expected $fclose_rx"
 	else
 		print_ok
@@ -1703,7 +1703,7 @@ chk_rm_nr()
 		count=$((count + cnt))
 		if [ "$count" != "$rm_subflow_nr" ]; then
 			suffix="$count in [$rm_subflow_nr:$((rm_subflow_nr*2))]"
-			extra_msg="$extra_msg simult"
+			extra_msg+=" simult"
 		fi
 		if [ $count -ge "$rm_subflow_nr" ] && \
 		   [ "$count" -le "$((rm_subflow_nr *2 ))" ]; then