Intro To 'stdbuf' Command In Linux

2023-07-05 - By Robert Elder

     I use the 'stdbuf' command to change the buffering behaviour of standard input and output:

stdbuf -o0 your-command-here

Example Use Case For 'stdbuf' Command

     Here, I have a C program in the file 'calm-down.c' that prints out a message to help people who have anxiety disorders:

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

int main(){
  while(1){
    printf(
      "\033[93mURGENT WARNING\033[0m: "
      "'\033[31;4mEVERYTHING IS FINE!!!\033[0m'\033[B\r"
    );
    usleep(500000);
  }
}

     If I compile and run this program like this:

gcc calm-down.c -o calm-down
./calm-down

     I don't see any output, even though my 'printf' statement will obviously run at least once.

     If I pipe the output of this program into the 'xxd' command like this:

./calm-down | xxd

     I still don't see any output! What's going on?  I'm starting to feel stressed out!

     It turns out that, by default, many programs that output to an interactive terminal use line based output buffering  Since the text in this program doesn't contain any newlines, the output simply accumulates in the buffer without showing up in the terminal.

     I can use this 'stdbuf' command to run my program with line based output buffering switched off:

stdbuf -o0 ./calm-down

     Now, when I run my program, I can see my helpful message:

     After reading the above message, all of my fears have now gone away!

Other Buffer Control Options

     The 'stdbuf' command includes even more buffering options for input and error streams.  It also allows you to control the buffers size, and explicitly switch to line-based buffering.  See the 'man' and 'info' pages for more information:

info stdbuf

man stdbuf

     And that's why the 'stdbuf' command is my favourite Linux command.