Python |执行并解析 Linux 命令

原文:https://www . geesforgeks . org/python-执行和解析-linux-commands/

先决条件:Linux Shell 和 Shell 脚本介绍

Linux 是目前最流行的操作系统之一，也是开发者的常用选择。它受欢迎是因为它是开源的，它是免费的和可定制的，它非常健壮和适应性强。

操作系统主要由两部分组成:内核和外壳。内核基本上处理软件和硬件之间的通信。外壳接受用户的输入或命令，并产生输出。现在大多数 Linux 发行版都使用 BASH 外壳(伯恩外壳)。Shell 命令和脚本非常强大，通常被开发人员使用。

在本文中，我们将研究使用 python 执行和解析 Linux 命令。

子流程–

子流程是 Python 中的一个模块，允许我们在 Python 中启动新的应用程序或流程。本模块旨在取代 python 中的几个旧模块。我们可以使用这个模块运行其他程序或者执行 Linux 命令。

开始一个过程–

使用子流程模块中定义的 Popen 函数可以产生一个新流程。它是 Popen 类的构造函数，接受参数来设置新的进程。本模块中的底层流程创建和管理由 Popen 类处理。

论据:

1. The first parameter is a list of commands and their options, if any. For example, ['ls', '-l'] The above example is equivalent to the terminal.

中输入‘ls-l’

• The second parameter is the stdout value. it specifies the standard output. ex: stdout = subprocess.PIPE This indicates that a new pipe or redirection should be created. The default value is “None”, which means that no redirection will occur.

  我们可以通过使用通信功能来检索命令的输出。它从 stdout 和 stderr 读取数据，直到到达文件结尾，并等待进程终止。它返回一个包含输出数据和错误(如果有)的元组。

  语法:

  py data = subprocess.Popen(['ls', '-l', filename], stdout = subprocess.PIPE) output = data.communicate()

  执行命令的输出存储在数据中。使用这些函数，我们可以执行 Linux 命令并获取它们的输出。

  列出目录–

  我们可以使用' ls '命令和选项，如'-l '，'-al '等来列出当前目录中的所有文件。然后，我们可以解析这个输出，并以可呈现的格式打印它。get_permissions()函数解析 list 命令的输出，只检索文件的名称及其对应的权限。

  ```py

  importing libraries

  import subprocess import os

  a function to list the files in

  the current directory and

  parse the output.

  def list_command(args = '-l'):

  # the ls command     cmd = 'ls'

  # using the Popen function to execute the     # command and store the result in temp.     # it returns a tuple that contains the      # data and the error if any.     temp = subprocess.Popen([cmd, args], stdout = subprocess.PIPE)

  # we use the communicate function     # to fetch the output     output = str(temp.communicate())

  # splitting the output so that     # we can parse them line by line     output = output.split("\n")

  output = output[0].split('\')

  # a variable to store the output     res = []

  # iterate through the output     # line by line     for line in output:         res.append(line)

  # print the output     for i in range(1, len(res) - 1):         print(res[i])

  return res

  parse the output of the ls

  command and fetch the permissions

  of the files and store them in

  a text file .

  def get_permissions():

  # get the output of the      # list command     res = list_command('-l')

  permissions = {}

  # iterate through all the rows     # and retrieve the name of the file     # and its permission.     for i in range(1, len(res) - 1):         line = res[i]

  line = line.split(' ')

  folder_name = line[len(line) - 1]         permission_value = line[0]

  permissions[folder_name] = permission_value

  # create a directory called     # outputs to store the output files     try:         os.mkdir('outputs')

  except:

  pass

  os.chdir('outputs')

  # open the output file     out = open('permissions.txt', 'w')

  out.write('Folder Name   Permissions\n\n')

  # write to the output file     for folder in permissions:

  out.write(folder + ' : ' + permissions[folder] + '\n')

  os.chdir('..')     return permissions

  if name == 'main':     list_command('-al') ```

  输出:

  Ping 命令–

  ping 命令代表数据包互联网协议。它最常用于检查两个系统或节点之间的连通性。使用 ping 命令，我们可以检查一个节点和另一个节点之间的连接是否正常。它在两个节点之间交换数据包，并计算往返时间。

  ```py

  importing libraries

  import subprocess import os

  a function to ping given host

  def ping(host):

  # command is pong     cmd = 'ping'

  # send two packets of data to the host     # this is specified by '-c 2' in the      # args list     temp = subprocess.Popen([cmd, '-c 2', host], stdout = subprocess.PIPE)

  # get the output of ping     output = str(temp.communicate())

  output = output.split("\n")

  output = output[0].split('\')

  # variable to store the result     res = []

  for line in output:         res.append(line)

  # print the results     print('ping results: ')     print('\n'.join(res[len(res) - 3:len(res) - 1]))

  return res

  if name == 'main':

  # ping google     ping('www.google.com') ```

  输出:

  更改权限–

  chmod 命令可用于更改文件权限。它是变更模式的缩写。更多信息可以在这里找到

  ```py

  importing libraries

  import subprocess import os

  functio to change the permissions

  of a given file

  def change_permissions(args, filename):

  # command name     cmd = 'chmod'

  # getting the permissions of     # the file before chmod     ls = 'ls'

  data = subprocess.Popen([ls, '-l', filename], stdout = subprocess.PIPE)

  output = str(data.communicate())

  print('file permissions before chmod % s: ' %(args))     print(output)

  # executing chmod on the specified file     temp = subprocess.Popen([cmd, args, filename], stdout = subprocess.PIPE)

  # getting the permissions of the      # file after chmod     data = subprocess.Popen([ls, '-l', filename], stdout = subprocess.PIPE)

  output = str(data.communicate())

  # printing the permissions after chmod     print('file permissions after chmod % s: ' %(args))     print(output)

  if name == 'main':

  # changing the permissions of 'sample.txt'      change_permissions('755', 'sample.txt') ```

  输出:

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