How to use Python regular expressions for container orchestration

In container orchestration, we often need to filter, match, and replace some information. Python provides regular expressions, a powerful tool that can help us complete these operations. This article will introduce how to use Python regular expressions for container orchestration, including basic knowledge of regular expressions, how to use the Python re module, and some common regular expression applications.

1. Basic knowledge of regular expressions

Regular Expression (Regular Expression) refers to a text pattern used to describe the structure of a type of string. In Python, we can use the re module to process regular expressions. Regular expressions consist of various characters, some of which have special meanings, as follows:

. Matches any character except newlines
^ Matches the beginning of a string
$ Matches characters End of string

• Match the previous character zero or more times
• Match the previous character one or more times
  ? Match the previous character zero or one time
  [] Matches any character contained in square brackets
  | Matches any one of two or more expressions

In addition to the above commonly used special characters, there are many others Special characters can be used as needed.

2. How to use the Python re module

Python's re module provides a series of functions to use regular expressions. Among them, the most common functions are re.findall(pattern, string) and re.sub(pattern, repl, string).

The re.findall(pattern, string) function is used to find all substrings in a string that match the regular expression and return a list. For example, if we want to find all numbers ending in an even number in a string, we can use the following code:

import re
text = '123 456 7890 23 45 6'
pattern = r'd*[02468]'
result = re.findall(pattern, text)
print(result)

The output result is:

['456', '7890', '6']

re.sub(pattern, repl, string) function uses Replaces the substring matching the regular expression in the string with the specified string and returns the replaced string. For example, if we want to replace all spaces in the string with hyphens "-", we can use the following code:

import re
text = 'hello world'
pattern = r's'
repl = '-'
result = re.sub(pattern, repl, text)
print(result)

The output result is:

'hello-world'

3. Common regular expression applications

1. Find the container name

In Docker, the container name often starts with "/", such as "/redis". We can use the following regular expression to search:

import re
text = '172.17.0.2 - - [15/May/2019:09:58:20 +0800] "GET /redis HTTP/1.1" 200 9876'
pattern = r'(?<=GETs)S+'
result = re.findall(pattern, text)
print(result)

The output result is:

['/redis']

Among them, the regular expression "(?<=GETs)S" means matching "GET" ( Note that there is a space after it.) A non-empty string beginning with.

2. Find the container IP address

In Docker, the container IP address usually starts with "172." We can use the following regular expression to search:

import re
text = '172.17.0.2 - - [15/May/2019:09:58:20 +0800] "GET /redis HTTP/1.1" 200 9876'
pattern = r'd{1,3}.d{1,3}.d{1,3}.d{1,3}'
result = re.findall(pattern, text)
print(result)

The output result is:

['172.17.0.2']

Among them, the regular expression "d{1,3}.d{1,3}.d{ 1,3}.d{1,3}" means matching a range of IP addresses.

3. Replace container name

In Docker, we often need to rename the container name. We can use the following regular expression to replace the container name:

import re
text = 'docker run -d --name redis01 redis'
pattern = r'--namesS+'
repl = '--name new_redis'
result = re.sub(pattern, repl, text)
print(result)

The output result is:

'docker run -d --name new_redis redis'

Among them, the regular expression "--namesS" means matching "--name" (note A non-empty string starting with a space); repl represents the string to be replaced.

Summary

Python regular expressions are a very common technology in container orchestration, which can help us filter, match, and replace some information. This article introduces the basic knowledge of Python regular expressions, how to use the re module, and some common regular expression applications. I hope it will be helpful to everyone's work in container orchestration.

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