output of dns-sd browse command not redirected to file in busybox shell(ash)

Question

To check if mdnsd is in probing mode we are using below command to browse for service and redirect its output a file, and hostname of the device is found in the command we decide that mdnsd is in probing mode.

command used for publishing service

dns-sd -R "Test status" "_mytest._tcp." "local." "22"

To browse the service following command is used (Running in background)

dns-sd -lo -Z _mytest._tcp > /tmp/myfile &

To display the content of the file used cat.

cat /tmp/myfile

myfile is empty, if > replaced with tee , I see output on console myfile remains empty.

I am unable to understand what is going on.

Is there any pointer, help

EDIT
Just for completeness adding output, which i missed adding before.

# dns-sd -lo -Z _mytest._tcp local
Using LocalOnly
Using interface -1
Browsing for _mytest._tcp
DATE: ---Tue 25 Apr 2017---
11:09:24.775  ...STARTING...

; To direct clients to browse a different domain, substitute that domain in place of '@'
lb._dns-sd._udp                                 PTR     @

; In the list of services below, the SRV records will typically reference dot-local Multicast DNS names.
; When transferring this zone file data to your unicast DNS server, you'll need to replace those dot-local
; names with the correct fully-qualified (unicast) domain name of the target host offering the service.

_mytest._tcp                                    PTR     Test\032status._mytest._tcp
Test\032status._mytest._tcp                     SRV     0 0 22 DevBoard.local. ; Replace with unicast FQDN of target host
Test\032status._mytest._tcp                     TXT     ""

Answer 1

You appear to have a program with behavior that differs based on whether its output is to a TTY. One workaround is to use a tool such as unbuffer or script to simulate a TTY.

Moreover, inasmuch as the use of a file at all is done as a workaround, I suggest using a FIFO to actually capture the line you want without needing to write to a file and poll that file's contents.

#!/bin/sh

newline='
'

# Let's define some helpers...
cleanup() {
  [ -e /proc/self/fd/3 ] && exec 3<&-                   ## close FD 3 if it's open
  rm -f "fifo.$$"                                       ## delete the FIFO from disk
  if [ -n "$pid" ] && kill -0 "$pid" 2>/dev/null; then  ## if our pid is still running...
    kill "$pid"                                         ## ...then shut it down.
  fi
}
die() { cleanup; echo "$*" >&2; exit 1; }

# Create a FIFO, and start `dns-sd` in the background *thinking* it's writing to a TTY
# but actually writing to that FIFO 
mkfifo "fifo.$$"
script -q -f -c 'dns-sd -lo -Z _mytest._tcp local' /proc/self/fd/1 |
  tr -d '\r' >"fifo.$$" & pid=$!

exec 3<"fifo.$$"

while read -t 1 -r line <&3; do
  case $line in
    "Script started on"*|";"*|"")  continue;;
    "Using "*|DATE:*|[[:digit:]]*) continue;;
    *)                             result="${result}${line}${newline}"; break
  esac
done

if [ -z "$result" ]; then
  die "Timeout before receiving a non-boilerplate line"
fi

printf '%s\n' "Retrieved a result:" "$result"
cleanup