subprocess模块
subprocess模块
subprocess主要用于提供执行系统命令的功能,其在python3中将commands、os.system,os.popen等功能全部集成了,所以在py3中推荐使用该模块
下面是可以执行shell命令的相关模块和函数:
os.system
os.spawn*
os.popen* --废弃
popen2.* --废弃
commands.* --废弃,3.x中被移除
常用方法
- subprocess.call() 执行命令,取出命令执行的结果,通常是shell返回的状态码,注意call会把执行结果打印出来,但是只会取执行结果的状态码
>>> import subprocess >>> res = subprocess.call('df -h',shell=True) Filesystem Size Used Avail Use% Mounted on /dev/vda3 19G 9.4G 8.2G 54% / tmpfs 3.9G 0 3.9G 0% /dev/shm /dev/vda1 194M 32M 153M 18% /boot >>> print(res) 0 >>> res = subprocess.call(['df', '-h'],shell=False) Filesystem Size Used Avail Use% Mounted on /dev/vda3 19G 9.4G 8.2G 54% / tmpfs 3.9G 0 3.9G 0% /dev/shm /dev/vda1 194M 32M 153M 18% /boot >>> print(res) 0 >>> res = subprocess.call('123',shell=True) /bin/sh: 123: command not found >>> print(res) 127
补充:
shell = True ,允许 shell 命令是字符串形式,否则,必须按列表形式传参数
- subprocess.check_call() 执行命令,如果执行状态码是 0 ,则返回0,否则抛异常。注意,如果命令执行成功,则subprocess.check_call()为0,否则subprocess.check_call()1没有值
>>> res1 = subprocess.check_call('free -m',shell=True) total used free shared buffers cached Mem: 7870 5217 2653 0 488 3108 -/+ buffers/cache: 1620 6250 Swap: 1023 0 1023 >>> print(res1) 0 >>> res2 = subprocess.check_call('123',shell=True) /bin/sh: 123: command not found Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/local/python3/lib/python3.5/subprocess.py", line 584, in check_call raise CalledProcessError(retcode, cmd) subprocess.CalledProcessError: Command '123' returned non-zero exit status 127 >>> print(res2) Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'res2' is not defined
- check_output 执行命令,如果状态码是 0 ,则返回执行结果,否则抛异常.
>>> res = subprocess.check_output('df -h',shell=True) >>> print(res) b'Filesystem Size Used Avail Use% Mounted on\n/dev/vda3 19G 9.4G 8.2G 54% /\ntmpfs 3.9G 0 3.9G 0% /dev/shm\n/dev/vda1 194M 32M 153M 18% /boot\n' >>> res1 = subprocess.check_output('dfaa',shell=True) /bin/sh: dfaa: command not found Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/local/python3/lib/python3.5/subprocess.py", line 629, in check_output **kwargs).stdout File "/usr/local/python3/lib/python3.5/subprocess.py", line 711, in run output=stdout, stderr=stderr) subprocess.CalledProcessError: Command 'dfaa' returned non-zero exit status 127 >>> print(res1) Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'res1' is not defined
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subprocess.Popen 执行复杂的命令
- Popen类:
class Popen(args, bufsize=0, executable=None, stdin=None, stdout=None, stderr=None, preexec_fn=None, close_fds=False, shell=False, cwd=None, env=None, universal_newlines=False, startupinfo=None, creationflags=0)
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参数说明:
- args:shell命令,可以是字符串或者序列类型(如:list,元组)
- bufsize:指定缓冲。0 无缓冲,1 行缓冲,其他 缓冲区大小,负值 系统缓冲
- stdin, stdout, stderr:分别表示程序的标准输入、输出、错误句柄
- preexec_fn:只在Unix平台下有效,用于指定一个可执行对象(callable object),它将在子进程运行之前被调用
- close_sfs:在windows平台下,如果close_fds被设置为True,则新创建的子进程将不会继承父进程的输入、输出、错误管道。所以不能将close_fds设置为True同时重定向子进程的标准输入、输出与错误(stdin, stdout, stderr)。
- shell:同上
- cwd:用于设置子进程的当前目录
- env:用于指定子进程的环境变量。如果env = None,子进程的环境变量将从父进程中继承。
- universal_newlines:不同系统的换行符不同,True -> 同意使用 \n
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startupinfo与createionflags只在windows下有效将被传递给底层的CreateProcess()函数,用于设置子进程的一些属性,如:主窗口的外观,进程的优先级等等
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执行普通命令:
>>> child = subprocess.Popen(['ping','-c','4','proxy.fuzengjie.cn']) >>> PING proxy.fuzengjie.cn (23.83.227.252) 56(84) bytes of data. 64 bytes from proxy.fuzengjie.cn (23.83.227.252): icmp_seq=1 ttl=48 time=188 ms 64 bytes from proxy.fuzengjie.cn (23.83.227.252): icmp_seq=2 ttl=48 time=184 ms 64 bytes from proxy.fuzengjie.cn (23.83.227.252): icmp_seq=3 ttl=48 time=184 ms 64 bytes from proxy.fuzengjie.cn (23.83.227.252): icmp_seq=4 ttl=48 time=184 ms --- proxy.fuzengjie.cn ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3273ms rtt min/avg/max/mdev = 184.661/185.637/188.307/1.544 ms >>>
从运行结果中看到,父进程在开启子进程之后并没有等待child的完成,而是直接运行print
还可以获取子进程的状况
* child.poll() # 检查子进程状态
* child.kill() # 终止子进程
* child.send_signal() # 向子进程发送信号
* child.terminate() # 终止子进程
* child.pid #子进程的pid
- 管道
可以在Popen()建立子进程的时候改变标准输入、标准输出和标准错误,并可以利用subprocess.PIPE将多个子进程的输入和输出连接在一起,构成管道(pipe)
import subprocess obj = subprocess.Popen(["python3"], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, universal_newlines=True) obj.stdin.write("print asd") obj.stdin.close() cmd_out = obj.stdout.read() obj.stdout.close() cmd_error = obj.stderr.read() obj.stderr.close() print(123) print(cmd_out) print(cmd_error) 输出: 123 File "<stdin>", line 2 print asd ^ SyntaxError: Missing parentheses in call to 'print'
subprocess.PIPE实际上为文本流提供一个缓存区。stdin 将标准输入放到缓冲区,系统执行完之后,会把标准输出和标准错误输出放到缓冲区,这样直接可以从缓冲区里拿出结果
- 父子进程通信
>>> import subprocess >>> child1 = subprocess.Popen('netstat -lnpt',shell=True,stdout=subprocess.PIPE) >>> child2 = subprocess.Popen(["grep","80"],stdin=child1.stdout, stdout=subprocess.PIPE) >>> print(child2.stdout.read()) b'tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 9804/nginx \n' >>> print(child2.stdout.read()) b'' >>> child1 = subprocess.Popen('netstat -lnpt',shell=True,stdout=subprocess.PIPE) >>> child2 = subprocess.Popen(["grep","80"],stdin=child1.stdout, stdout=subprocess.PIPE) >>> output = child2.communicate() >>> print(output) (b'tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 9804/nginx \n', None) >>> print(output) (b'tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 9804/nginx \n', None) >>> output = child2.communicate() Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/local/python3/lib/python3.5/subprocess.py", line 1055, in communicate stdout = self.stdout.read() ValueError: read of closed file
child1的stdout将文本输出到缓存区,随后child2的stdin从该PIPE中将文本读取走。child2的输出文本也被存放在PIPE中,直到communicate()方法从PIPE中读取出PIPE中的文本、注意:communicate()是Popen对象的一个方法,该方法会阻塞父进程,直到子进程完成。