Python 3: Handling stdin, stderr and stdout with subprocess

20 Jun 2020

I don’t like using subprocess that often. Using subprocess to invoke curl instead of using requests is not how you should use it. But there are valid exceptions.

Below example, I write to the stdin and then read stdout and stderr.

from subprocess import Popen, PIPE

try:
    command = ["awk", "-F ", "{print  $2}"]
    process = Popen(command,
                    stdin=PIPE,
                    stdout=PIPE,
                    stderr=PIPE,
                    universal_newlines=True)
    process.stdin.write("column1 column2 column3\ndata1 data2 data3")
    process.stdin.close()
    process.wait()

    print("Process exited with " + str(process.returncode))
    print("Printing standard output")
    print(str(process.stdout.read()))
    print("Printing standard error")
    print(str(process.stderr.read()))
except FileNotFoundError:
    print("Program not found")

This is the output.

Process exited with 0
Printing standard output
column2
data2

Printing standard error

Python 3: Handling stdin, stderr and stdout with subprocess

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