CODEWITHSUNDEEP
bashtcp
dereker
dereker

Reputation: 1

How can I run a script inside TCP session

I want to create a script that uses a couple arguments from the TCP output and prints something back to the TCP input.

I'm trying to solve this with bash, I tried:

exec 3<>/dev/tcp/url/port;
msg=$(head -2 <&3)
arg1=$( some grep and sed operation on msg) #is a number
arg2=$( some grep and sed operation on msg) #is a string
counter=0
while [ $counter -lt $arg1 ]
do
    #here I want to print something to netcat input
    echo "$arg2 sometext" >&3;
    ((counter++))
done
#then print the awnser from the server
cat <&3

But the script can't write back to netcat input. (No error, ist just does nothing after echo "$arg2 sometext" >&3 )

Upvotes: 0

Views: 241

Answers (1)

Charles Duffy
Charles Duffy

Reputation: 295530

Fewer headaches if you avoid /dev/tcp and use socat to run your code with stdin and stdout connected to the socket.

myfunc() {
  local msg msg1 msg2 arg1 arg2 counter
  IFS= read -r msg1 # first line of msg
  IFS= read -r msg2 # second line of msg

  msg="$msg1"$'\n'"$msg2"

  # FYI: There are usually better ways to do string manipulation in bash than grep/sed/etc
  arg1=$(do-something-with "$msg" </dev/null)
  arg2=$(do-something-with "$msg" </dev/null)

  for (( counter=0; counter<arg1; counter++ )); do
    echo "$arg2 sometext"
  done
  cat >&2  # write to stderr, since anything to stdout will go to the remote socket
}
export -f myfunc

socat TCP:"$host":"$port" "SYSTEM:bash -xc myfunc"

Upvotes: 1

Related Questions