Echo Client
This implements a client that opens a server connection, sends messages from stdin, receives server replies and sends them to stdout. 
#!/usr/local/bin/tclsh7.5

# Read data from a channel (the server socket) and put it to stdout
# this implements receiving and handling (viewing) a server reply 
proc read_sock {sock} {
  set l [gets $sock]
  puts stdout "ServerReply:$l"
}

# Read a line of text from stdin and send it to the echoserver socket,
# on eof stdin closedown the echoserver client socket connection
# this implements sending a message to the Server.
proc read_stdin {wsock} {
  global  eventLoop
  set l [gets stdin]
  if {[eof stdin]} {
    close $wsock             ;# close the socket client connection
    set eventLoop "done"     ;# terminate the vwait (eventloop)
  } else {
    puts $wsock $l           ;# send the data to the server
  }
}

# open the connection to the echo server...
set eshost "scoda"
set esport 9999

# this is a synchronous connection: 
# The command does not return until the server responds to the 
#  connection request
set esvrSock [socket $eshost $esport]

#if {[eof $esvrSock]} { # connection closed .. abort }

# Setup monitoring on the socket so that when there is data to be 
# read the proc "read_sock" is called
fileevent $esvrSock readable [list read_sock $esvrSock]

# configure channel modes
# ensure the socket is line buffered so we can get a line of text 
# at a time (Cos thats what the server expects)...
# Depending on your needs you may also want this unbuffered so 
# you don't block in reading a chunk larger than has been fed 
#  into the socket
# i.e fconfigure $esvrSock -blocking off

fconfigure $esvrSock -buffering line

# set up our keyboard read event handler: 
#   Vector stdin data to the socket
fileevent stdin readable [list read_stdin $esvrSock]

# message indicating connection accepted and we're ready to go 
puts "EchoServerClient Connected to echo server"
puts "...what you type should be echoed."

# wait for and handle either socket or stdin events...
vwait eventLoop

puts "Client Finished"


Another option is to do an asynchronous client connection 

set esvrSock [socket -async $eshost $esport]

# .... do whatever that we can't connect synchronously... 

# resync with the connection, 
#Socket becomes writable when connection available
fileevent $esvrSock writable { set connect 1 }
vwait connect   
    # will 'block' here till connection up (or eof or error)

fileevent $esvrSock writable {}    ;# remove previous handler

if {[eof $esvrSock]} { # connection closed .. abort }

# set translation, buffering  and/or blocking modes
fconfigure $esvrSock -translation {auto crlf} -buffering line
    ...



--------------------------------------------------------------------------------

Echo Server
Server that reflects its client messages back to the source 

#!/usr/local/bin/tclsh7.5

set svcPort 9999

# Implement the service
# This example just writes the info back to the client...
proc doService {sock msg} {
    # puts $sock "echosrv:$l"
     puts $sock "$l"
}

# Handles the input from the client and  client shutdown
proc  svcHandler {sock} {
  set l [gets $sock]    ;# get the client packet
  if {[eof $sock]} {    ;# client gone or finished
     close $sock        ;# release the servers client channel
  } else {
    doService $sock $l
  }
}

# Accept-Connection handler for Server. 
# called When client makes a connection to the server
# Its passed the channel we're to communicate with the client on, 
# The address of the client and the port we're using
#
# Setup a handler for (incoming) communication on 
# the client channel - send connection Reply and log connection
proc accept {sock addr port} {
  
  # if {[badConnect $addr]} {
  #     close $sock
  #     return
  # }

  # Setup handler for future communication on client socket
  fileevent $sock readable [list svcHandler $sock]

  # Read client input in lines, disable blocking I/O
  fconfigure $sock -buffering line -blocking 0

  # Send Acceptance string to client
  puts $sock "$addr:$port, You are connected to the echo server."
  puts $sock "It is now [exec date]"

  # log the connection
  puts "Accepted connection from $addr at [exec date]"
}


# Create a server socket on port $svcPort. 
# Call proc accept when a client attempts a connection.
socket -server accept $svcPort
vwait events    ;# handle events till variable events is set


I can not send/receive message from client/server