63

Is there a filter which I could use to rate-limit a pipe on linux? If this exists, let call it rate-limit, I want to be able to type in a terminal something like

cat /dev/urandom | rate-limit 3 -k | foo

in order to send a a stream of random bytes to foo's standard input at a rate (lower than) 3 kbytes/s.

migrated from stackoverflow.com Jan 31 '11 at 10:51

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  • 1
    I asked here because I want to use it in a programme, not for troubleshooting. But it's my very first question here so I apologize if I made an error. – Frédéric Grosshans Mar 17 '10 at 17:54
  • 1
    BTW, the above is an unnecessary use of cat, you could do rate-limit 3k < /dev/urandom | foo. – dmckee Mar 17 '10 at 18:15
88

Pipe Viewer has this feature.

cat /dev/urandom | pv -L 3k | foo
  • 1
    Also handy to use while watching output of a job, with -q... e.g: command 2>&1 | pv -q -L 3k – Attie Oct 19 '17 at 12:00
17

I'd say that Juliano has got the right answer if you have that tool, but I'd also suggest that this is a neat little K&R style exercise: just write a specialized version of cat that reads one character at a time from stdin, outputs each to stdout and then usleeps before moving on. Be sure to unbuffer the standard output, or this will run rather jerkily.

I called this slowcat.c:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char**argv){
  int c;
  useconds_t stime=10000; // defaults to 100 Hz

  if (argc>1) { // Argument is interperted as Hz
    stime=1000000/atoi(argv[1]);
  }

  setvbuf(stdout,NULL,_IONBF,0);

  while ((c=fgetc(stdin)) != EOF){
    fputc(c,stdout);
    usleep(stime);
  }

  return 0;
}

Compile it and try with

$ ./slowcat 10 < slowcat.c
  • 17
    Now I'm feeling the horrible temptation to add a "clack" noise to each character an set the default speed to 40 CPS, with an extra delay for newlines. – dmckee Mar 17 '10 at 19:19
  • I'd use that with one of those retro terminal screensavers for a giggle if I had speakers attached to my linux boxes. – Benny Mackney Oct 4 '16 at 23:07
4

throttle seems designed specifically for this. e.g.

cat /dev/urandom | throttle -k 3 | foo
  • 1
    I would agree with this, but there doesn't seem to be a standard package for Ubuntu. I also am not seeing the source code for it either. Anyone know where you can get this utility? – Benjamin Leinweber Feb 17 '17 at 16:08
  • 1
    @BenjaminLeinweber It looks like the website that normally hosts the code is offline, but freebsd has the source for 1.2 available on their ftp server. You would have to download it there & ./configure && make. – Ponkadoodle Feb 17 '17 at 21:34
3

Here's an all-shell solution that won't lose input (cf. the head -1 idea from Mike S):

hexdump -c /dev/urandom | (lines=0; while read line; do echo $line; if [ $((++lines % 10)) -eq 0 ]; then sleep 1; fi; done) | cat -n
2

Quick and dirty, all shell all the time (I have CentOS and pv doesn't come with it by default):

hexdump -c /dev/urandom | while true; do head -1; sleep 1; done | \
your_program_that_reads_stdin  -your_argument_list

...dirty because although it's rate limited, it's bursty at a rate that I can't tell you :-) . But it's handy when you just need to send data from one place to the other (I was doing some socat tests) and you don't want to swamp your screen with garbage.

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