[Richard Suchenwirth] 2006-02-28 - The following very simple script can act as either the server or the client of a [socket] connection:
   * When called with "server" as first argument, it listens on the given port. Lines coming in are evaluated, and the result is sent back
   * Otherwise, the script is a client: takes lines from stdin, sends them to the server, displays the result

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 set host localhost
 set port 9900

 if {[lindex $argv 0] eq "server"} {
    puts "Server started..."
    socket -server server $port
 } else {
    set chan [socket $host $port]
    fconfigure $chan -buffering line
    fileevent $chan readable [list client'read $chan]
    fileevent stdin readable [list client'send $chan]
 }
#-----------------------------------------------------
 proc server {chan addr port} {
    fconfigure $chan -buffering line
    while {[gets $chan line]>=0} {
	catch $line res
	puts $line->$res ;# local logging
	puts $chan $res
    }
    close $chan
 }
#------------------------------------------------------
 proc client'read chan {
    if {[eof $chan]} {close $chan; exit}
    gets $chan line
    puts <-$line
 }
 proc client'send chan {
    gets stdin line
    puts $chan $line
 }
#------------------------------------------------------
 vwait forever

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[Category Example] - [Arts and crafts of Tcl-Tk programming]