Is there a shell command to delay a buffer?

Question

I am looking for a shell command X such as, when I execute:

command_a | X 5000 | command_b

the stdout of command_a is written in stdin of command_b (at least) 5 seconds later.

A kind of delaying buffer.

As far as I know, buffer/mbuffer can write at constant rate (a fixed number of bytes per second). Instead, I would like a constant delay in time (t=0 is when X read a command_a output chunk, at t=5000 it must write this chunk to command_b).

[edit] I've implemented it: https://github.com/rom1v/delay

Answer 1

As it seemed such a command dit not exist, I implemented it in C: https://github.com/rom1v/delay

delay [-b <dtbufsize>] <delay>

Answer 2

This might work

time_buffered () {
   delay=$1
   while read line; do
       printf "%d %s\n" "$(date +%s)" "$line"
   done | while read ts line; do
       now=$(date +%s)
       if (( now - ts < delay)); then
           sleep $(( now - ts ))
       fi
       printf "%s\n" "$line"
   done
}

commandA | time_buffered 5 | commandB

The first loop tags each line of its input with a timestamp and immediately feeds it to the second loop. The second loop checks the timestamp of each line, and will sleep if necessary until $delay seconds after it was first read before outputting the line.