execnsnoop - not all cat have -v

[vanhauser-thc]

busybox and other cat tools do not have -v, added a check if the option is present

--- bin/execsnoop
+++ bin/execsnoop
@@ -58,6 +58,7 @@ tracing=/sys/kernel/debug/tracing
 flock=/var/tmp/.ftrace-lock; wroteflock=0
 opt_duration=0; duration=; opt_name=0; name=; opt_time=0; opt_reexec=0
 opt_argc=0; argc=8; max_argc=16; ftext=
+VOPT=-v
 trap ':' INT QUIT TERM PIPE HUP        # sends execution to end tracing section

 function usage {
@@ -156,6 +157,9 @@ else
        fi
 fi

+# not all cat have -v, e.g busybox
+echo test | cat -v 2> /dev/null | grep -q test || VOPT=
+
 ### check permissions
 cd $tracing || die "ERROR: accessing tracing. Root user? Kernel has FTRACE?
     debugfs mounted? (mount -t debugfs debugfs /sys/kernel/debug)"
@@ -224,10 +228,10 @@ warn "echo > trace"
 ( if (( opt_duration )); then
        # wait then dump buffer
        sleep $duration
-       cat -v trace
+       cat $VOPT trace
 else
        # print buffer live
-       cat -v trace_pipe
+       cat $VOPT trace_pipe
 fi ) | $awk -v o=$offset -v opt_name=$opt_name -v name=$name \
     -v opt_duration=$opt_duration -v opt_time=$opt_time -v kname=$kname \
     -v opt_reexec=$opt_reexec '