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0

I'm trying to write a simple python script that reads from a fifo and then writes to another fifo.

I have created two FIFOs using the following command:

$ mkfifo input

$ mkfifo output

I invoke the script using the following command:

$ tail -f input | stdbuf -oL ../entropyCalc/entropy.py > output

, observe the FIFO output using:

$ tail -f output

and then invoke a writer using the following command:

$ echo "/path/to/a/valid/file" >> input

The problem is I expect the fifo to output the result as soon as it processes the input file, but I only observe that when I invoke (execute) the script once, exit and then re-execute the script. Everything works fine after this.

In summary:

I don't see any output in the reader if I execute script -> spin up reader -> write to input fifo

But, the command tail -f output outputs the result when I execute the script -> spin up the reader -> write to fifo -> kill script -> re-execute the script

I'm not sure what causes this behaviour since I'd expect the system to write to the files as soon as the result is written to stdout. I'd have expected the buffering if I would not used stdbuf -oL which limits buffering to a line.

The python script is a simple entropy calculator:

#! /usr/bin/env python2



import sys, os

import numpy as np

from scipy.stats import entropy



while 1:

    try:

        line = sys.stdin.readline()

    except KeyboardInterrupt:

        break



    if not line:

        break



    line = line.strip()



    if not line == '':

        fname1 = open(line)

        fsize = os.path.getsize(line)

        f1 = np.frombuffer(fname1.read(fsize), dtype=np.uint8)

        value,counts = np.unique(f1, return_counts=True)

        print line,str(entropy(counts))

        sys.stdout.flush()

I'm using bash 4.4 on Ubuntu 18.04.3

linux bash ubuntu pipe fifo

share|improve this question

edited 10 mins ago

lol

asked 41 mins ago

lollol

2366 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You have unbuffered the script but not tail. Why not? unix.stackexchange.com/a/423645/70524
  
  – muru
  4 mins ago
  

  
  
  
  

add a comment
 | 

0

I'm trying to write a simple python script that reads from a fifo and then writes to another fifo.

I have created two FIFOs using the following command:

$ mkfifo input

$ mkfifo output

I invoke the script using the following command:

$ tail -f input | stdbuf -oL ../entropyCalc/entropy.py > output

, observe the FIFO output using:

$ tail -f output

and then invoke a writer using the following command:

$ echo "/path/to/a/valid/file" >> input

The problem is I expect the fifo to output the result as soon as it processes the input file, but I only observe that when I invoke (execute) the script once, exit and then re-execute the script. Everything works fine after this.

In summary:

I don't see any output in the reader if I execute script -> spin up reader -> write to input fifo

But, the command tail -f output outputs the result when I execute the script -> spin up the reader -> write to fifo -> kill script -> re-execute the script

I'm not sure what causes this behaviour since I'd expect the system to write to the files as soon as the result is written to stdout. I'd have expected the buffering if I would not used stdbuf -oL which limits buffering to a line.

The python script is a simple entropy calculator:

#! /usr/bin/env python2



import sys, os

import numpy as np

from scipy.stats import entropy



while 1:

    try:

        line = sys.stdin.readline()

    except KeyboardInterrupt:

        break



    if not line:

        break



    line = line.strip()



    if not line == '':

        fname1 = open(line)

        fsize = os.path.getsize(line)

        f1 = np.frombuffer(fname1.read(fsize), dtype=np.uint8)

        value,counts = np.unique(f1, return_counts=True)

        print line,str(entropy(counts))

        sys.stdout.flush()

I'm using bash 4.4 on Ubuntu 18.04.3

linux bash ubuntu pipe fifo

share|improve this question

edited 10 mins ago

lol

asked 41 mins ago

lollol

2366 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You have unbuffered the script but not tail. Why not? unix.stackexchange.com/a/423645/70524
  
  – muru
  4 mins ago
  

  
  
  
  

add a comment
 | 

I'm trying to write a simple python script that reads from a fifo and then writes to another fifo.

I have created two FIFOs using the following command:

$ mkfifo input

$ mkfifo output

I invoke the script using the following command:

$ tail -f input | stdbuf -oL ../entropyCalc/entropy.py > output

, observe the FIFO output using:

$ tail -f output

and then invoke a writer using the following command:

$ echo "/path/to/a/valid/file" >> input

The problem is I expect the fifo to output the result as soon as it processes the input file, but I only observe that when I invoke (execute) the script once, exit and then re-execute the script. Everything works fine after this.

In summary:

I don't see any output in the reader if I execute script -> spin up reader -> write to input fifo

But, the command tail -f output outputs the result when I execute the script -> spin up the reader -> write to fifo -> kill script -> re-execute the script

I'm not sure what causes this behaviour since I'd expect the system to write to the files as soon as the result is written to stdout. I'd have expected the buffering if I would not used stdbuf -oL which limits buffering to a line.

The python script is a simple entropy calculator:

#! /usr/bin/env python2



import sys, os

import numpy as np

from scipy.stats import entropy



while 1:

    try:

        line = sys.stdin.readline()

    except KeyboardInterrupt:

        break



    if not line:

        break



    line = line.strip()



    if not line == '':

        fname1 = open(line)

        fsize = os.path.getsize(line)

        f1 = np.frombuffer(fname1.read(fsize), dtype=np.uint8)

        value,counts = np.unique(f1, return_counts=True)

        print line,str(entropy(counts))

        sys.stdout.flush()

I'm using bash 4.4 on Ubuntu 18.04.3

linux bash ubuntu pipe fifo

share|improve this question

edited 10 mins ago

lol

asked 41 mins ago

lollol

2366 bronze badges

$ mkfifo input

$ mkfifo output

$ tail -f input | stdbuf -oL ../entropyCalc/entropy.py > output

$ tail -f output

$ echo "/path/to/a/valid/file" >> input

#! /usr/bin/env python2



import sys, os

import numpy as np

from scipy.stats import entropy



while 1:

    try:

        line = sys.stdin.readline()

    except KeyboardInterrupt:

        break



    if not line:

        break



    line = line.strip()



    if not line == '':

        fname1 = open(line)

        fsize = os.path.getsize(line)

        f1 = np.frombuffer(fname1.read(fsize), dtype=np.uint8)

        value,counts = np.unique(f1, return_counts=True)

        print line,str(entropy(counts))

        sys.stdout.flush()

share|improve this question

edited 10 mins ago

lol

asked 41 mins ago

lollol

2366 bronze badges

share|improve this question

edited 10 mins ago

lol

asked 41 mins ago

lollol

2366 bronze badges

asked 41 mins ago

lollol

2366 bronze badges

asked 41 mins ago

lollol

2366 bronze badges