保存子进程命令的错误信息

问题描述

当使用子进程运行 bash 命令时，我可能会遇到命令无效的情况.在这种情况下，bash 将返回错误消息.我们怎样才能捕捉到这个消息?我想将此消息保存到日志文件中.以下是一个示例，我尝试列出不存在目录中的文件.

When running bash command using subprocess, I might run into situation where the command is not valid. In this case, bash would return an error messsage. How can we catch this message? I would like to save this message to a log file. The following is an example, where I try to list files in a non-existed directory.

try:
    subprocess.check_call(["ls", "/home/non"]) 
    df = subprocess.Popen(["ls", "/home/non"], stdout=subprocess.PIPE)        
    output, err = df.communicate()
    # process outputs
except Exception as error:        
    print error
    sys.exit(1)

Bash 会打印ls: cannot access/home/non: No such file or directory".我怎样才能得到这个错误信息?except 行捕获的错误明显不同，它说命令'['ls'，'/home/non']'返回非零退出状态2".

Bash would prints "ls: cannot access /home/non: No such file or directory". How can I get this error message? The error caught by the except line is clearly different, it says "Command '['ls', '/home/non']' returned non-zero exit status 2".

推荐答案

你可以将stderr重定向到一个文件对象:

You can redirect stderr to a file object:

from subprocess import PIPE, CalledProcessError, check_call, Popen

with open("log.txt", "w") as f:
    try:
        check_call(["ls", "/home/non"], stderr=f)
        df = Popen(["ls", "/home/non"], stdout=PIPE)
        output, err = df.communicate()
    except CalledProcessError as e:
        print(e)
        exit(1)

输出到 log.txt:

Output to log.txt:

ls: cannot access /home/non: No such file or directory

如果你想要在except中的消息:

If you want the message in the except:

try:
    check_call(["ls", "/home/non"])
    df = Popen(["ls", "/home/non"], stdout=PIPE)
    output, err = df.communicate()
except CalledProcessError as e:
    print(e.message)

对于 python 2.6，e.message 将不起作用.您可以使用 python 2.7 的 check_output 的类似版本，该版本适用于 python 2.6:

For python 2.6 the e.message won't work. You can use a similar version of python 2.7's check_output that will work with python 2.6:

from subprocess import PIPE, CalledProcessError, Popen

def check_output(*args, **kwargs):
    process = Popen(stdout=PIPE, *args, **kwargs)
    out, err = process.communicate()
    ret = process.poll()
    if ret:
        cmd = kwargs.get("args")
        if cmd is None:
            cmd = args[0]
        error = CalledProcessError(ret, cmd)
        error.out = out
        error.message = err
        raise error
    return out

try:
    out = check_output(["ls", "/home"], stderr=PIPE)
    df = Popen(["ls", "/home/non"], stdout=PIPE)
    output, err = df.communicate()
except CalledProcessError as e:
    print(e.message)
else:
    print(out)

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