Source: https://stackoverflow.com/a/19271368
You can achieve it in two steps:
1) You need to start nc with a named pipe (fifo) as its input:
mkfifo /tmp/fifoIn; cat /tmp/fifoIn | nc localhost 2222 &
2) Send your data from file input.txt, line by line with 2 sec delay:
cat input.txt | while read line; do echo $line; sleep 2; done > /tmp/fifoIn
I've tested it with this "server" (I'm using openbsd netcat syntax):
nc -l localhost 2222
If you don't want the new-line char after every line use echo -n instead of echo.