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Awk implements SQL like join operation

2020-11-07 18:55:49 Irving the procedural ape

awk、grep and sed go by the name of linux Three swordsmen , in fact grep and awk I also use it in my daily work (sed Use less ), Maybe some people are right about awk Less understanding , Let me give you a general introduction to . Many people think awk It's just a text processing tool , In fact, they use it the same way . But it's actually a language , Have mathematical operators 、 Process control statements , It even encapsulates many built-in variables and functions for text processing , This makes it powerful in text processing . If grep Can only do data filtering , that awk It can also process data 、 Analyze and even generate reports , After all, it's a complete programming language .

Because this article is not awk Getting started with , If you want to get started, I recommend Ruan Yifeng awk Introductory tutorial and Left ear mouse AWK A concise tutorial .

Back to my topic today , Today I'd like to show you something I use a lot awk Scene . Because we do back-end development , Often when doing data analysis, there will be such a problem ,1. Facing hundreds of thousands of data , We need to screen out hundreds and thousands of specific key The data of .2. For these millions of data , Directed against id Fields complement other fields .

There may be mastery of excel My classmates jumped out and said “ Is this ,so easy,vlookup That's it !” , in fact ,excel It does solve the problem , But it's a little heavy , Even sometimes we can't use it on the server excel. What other ways ? For the two scenes I'm talking about , Actually, think about it , Is it right? sql Two watches in Chinese join Can solve the problem . In fact, you don't really need to put files in the database , Only need to use awk One order can solve .

example

Let's take the question like , Suppose there are two files ,score.txt Save the student number + Performance data , Another one name.txt Save the student number + Name data , Now you want to know how many points everyone has baked .

score.txt

id score 1 872 673 684 755 906 1007 0

name.txt

id name 1  Zhang San 2  Li Si 3  Wang Wu 4  Zhao er 5  Lennon 6  Big bear 

You want a copy with a student number Name and grade data , It looks like this .

id score name 1 87  Zhang San 2 67  Li Si 3 68  Wang Wu 4 75  Zhao er 5 90  Lennon 6 100  Big bear 7 0

use awk How easy it is to generate such data ? Just one line of code , You can save name.txt and score.txt, And then execute the following command to try .

awk 'ARGV[1]==FILENAME {map[$1]=$2} ARGV[2]==FILENAME {print $0, map[$1]}' name.........

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