sh python模块如何记录stderr / stdout并仅捕获stdout？

Question

Using the sh module, I would like to log the stdout/stderr of the process and capture stdout for processing. The process may take a long time and logging must not wait until the process is finished so the user sees the output in real time.

The following works fine to log stdout/stderr. But stdout is mixed with stderr and there is no convenient way to separate one from the other.

import sh
import logging

logger = logging.getLogger(__name__)

command = sh.bash('-c', 'echo a; echo b >&2', _iter=True, _err_to_out=True)

for line in command:
    logger.error(line)

print(command.stdout)

the output is like this:

a
b
b'a\nb\n'

Is there a way to do the same but without mixing stdout and stderr ?

Answer 1

The solution is to set _out and _err to the desired logging function ( logging.error for instance). It will be called as soon as a new line is read from either stderr or stdout and the user will be shown the output incrementally.

When _out or _err are set, however, sh does not collect the output and it will not be available for processing. This is what _tee=True is for: it collects stdout and stderr even when _out or _err are set.

import sh
import logging

logger = logging.getLogger(__name__)

command = sh.bash('-c', 'echo a; echo b >&2',
                  _tee=True,
                  _out=lambda x: logger.error(x.strip()),
                  _err=lambda x: logger.error(x.strip()))

print(command.stdout)

the output is

a
b
b'a\n'