tests: prune remaining xargs(1), add missing zfs-project -c0 note

-c0 suppresses diagnoses ‒ it's not just -c but with NULs; cf.
  http://build.zfsonlinux.org/builders/Debian%2010%20x86_64%20%28TEST%29/builds/10605/steps/shell_4/logs/log
search for the second "zfs project -s -p" instance

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12979

tests/zfs-tests/include/commands.cfg

@@ -109,8 +109,7 @@ export SYSTEM_FILES_COMMON='arp
     vmstat
     wait
     wc
-    which
-    xargs'
+    which'
 
 export SYSTEM_FILES_FREEBSD='chflags
     compress

tests/zfs-tests/tests/functional/alloc_class/alloc_class_012_pos.ksh

@@ -33,7 +33,7 @@ function file_in_special_vdev # <dataset> <inode>
 {
 	typeset dataset="$1"
 	typeset inum="$2"
-	typeset num_normal=$(echo $ZPOOL_DISKS | wc -w | xargs)
+	typeset num_normal=$(echo $ZPOOL_DISKS | wc -w)
 
 	zdb -dddddd $dataset $inum | awk -v d=$num_normal '{
 # find DVAs from string "offset level dva" only for L0 (data) blocks

tests/zfs-tests/tests/functional/cli_root/zdb/zdb_object_range_pos.ksh

@@ -142,8 +142,8 @@ log_must test "\n$actual\n" == "\n$expected\n"
 # Specifying individual object IDs works
 objects="$start1 $end1 $start2 $end2"
 expected="$objects"
-actual=$(get_object_list $TESTPOOL/$TESTFS $objects | awk '{print $1}' | xargs)
-log_must test "$actual" == "$expected"
+actual=$(get_object_list $TESTPOOL/$TESTFS $objects | awk '{print $1}' | tr '\n' ' ')
+log_must test "${actual% }" == "$expected"
 
 # Get all objects in the meta-objset to test m (spacemap) and z (zap) flags
 all_mos_objects=$(get_object_list $TESTPOOL 0:-1)

tests/zfs-tests/tests/functional/cli_root/zpool_add/zpool_add.kshlib

@@ -57,7 +57,7 @@ function find_mnttab_dev
 	if is_freebsd; then
 		# FreeBSD doesn't have a mnttab file.
 		mount -p | awk -v dir="^${DEV_DSKDIR}" \
-		    '$1 ~ dir { print $1 }' | xargs
+		    '$1 ~ dir { print $1 }'
 		return 0
 	elif is_linux; then
 		typeset mnttab="/etc/mtab"

tests/zfs-tests/tests/functional/cli_root/zpool_events/zpool_events_clear.ksh

@@ -43,7 +43,7 @@ for i in `seq 1 $EVENTS_NUM`; do
 done
 # wait a bit to allow the kernel module to process new events
 zpool_events_settle
-EVENTS_NUM=$(zpool events -H | wc -l | xargs)
+EVENTS_NUM=$(zpool events -H | wc -l)
 
 # 3. Verify 'zpool events -c' successfully clear new events
 CLEAR_OUTPUT=$(zpool events -c)

tests/zfs-tests/tests/functional/mv_files/mv_files_common.kshlib

@@ -152,8 +152,7 @@ function generate_files
 #
 function mv_files
 {
-        find $1 -type f -print | xargs -I "{}" \
-                mv {} $2 > /dev/null 2>&1
+        find $1 -type f -exec mv {} $2 \; > /dev/null 2>&1
 }
 
 #
@@ -165,8 +164,7 @@ function mv_files
 function count_files
 {
         typeset -i file_num
-        file_num=`find $1  -type f -print | \
-                wc -l`
+        file_num=$(find $1 -type f -print | wc -l)
         (( file_num != $2 )) && \
                 log_fail "The file number of target directory"\
                         "$2 is not equal to that of the source "\

tests/zfs-tests/tests/functional/projectquota/projecttree_002_pos.ksh

@@ -109,8 +109,7 @@ log_must eval "zfs project -cr $PRJDIR/a1/a2 | grep a3 | grep 'not set'"
 log_must eval "zfs project -cr $PRJDIR/a1/a2 | grep d4 | grep 'not set'"
 log_must eval "zfs project $PRJDIR/a1/a2/a3/d4 | grep '0 \-'"
 
-log_must eval \
-    "zfs project -cr -0 $PRJDIR/a1/a2 | xargs -0 zfs project -s -p $PRJID2"
+log_must eval "zfs project -s -p $PRJID2 $(zfs project -cr0 $PRJDIR/a1/a2 | tr '\0' '\t')"
 log_mustnot eval "zfs project -cr $PRJDIR/a1/a2 | grep a3 | grep 'not set'"
 log_mustnot eval "zfs project -cr $PRJDIR/a1/a2 | grep d4 | grep 'not set'"