Python read stdin arguments from pipe

pipetest.md

Pipetest

clitest and stdin don't always work well together. StackOverflow wasn't much help (shocked pikachu)! Buried deep in the interwebs is the bash advice to check for a TTY and whether stdin was piped with this: if [ ! -t 0 ] && [ -p /dev/stdin ];. Using this, I wanted to see how to do something similar in Python to make clitest work. Even deeper on the internet was this gem, which led me to the answer - use stat in Python to test whether stdin is a FIFO (pipe).

Thus, the answer to this hours long search is simply this function:

def stdin_is_piped():
    fileno = sys.stdin.fileno()
    mode = os.fstat(fileno).st_mode
    return not os.isatty(fileno) and stat.S_ISFIFO(mode)

With this, now we can run clitests on Python utilities that pipe arguments from stdin.

$ echo x y z | ./bin/pipetest a b c
arg: a
arg: b
arg: c
stdin: x y z
$

$ ./bin/pipetest a b c
arg: a
arg: b
arg: c
no piped data!
$

$ ./bin/pipetest
no piped data!
$

pipetest.py

#!/usr/bin/env python3

import os
import stat
import sys

def stdin_is_piped():
    fileno = sys.stdin.fileno()
    mode = os.fstat(fileno).st_mode
    return not os.isatty(fileno) and stat.S_ISFIFO(mode)

if __name__ == "__main__":
    for arg in sys.argv[1:]:
        print("arg: {}".format(arg))
    if stdin_is_piped():
        for line in sys.stdin.read().splitlines():
            print("stdin: {}".format(line))
    else:
        print("no piped data!")