[one day learning awk] Fundamentals

1. awk What is it ？

awk yes linux Environment , A syntax sugar similar to regular expressions in code .

2. awk Statement composition of

 awk The sentence of is mainly divided into three parts ：

One is BEGIN, This part mainly completes initialization , Only once , not essential .

Then there is the repeated part ,repeat. This section performs a corresponding operation for each match .

And finally END part , Generally, the closing operation is completed , Only once , not essential .

3. Try to use BEGIN

First , We create a text ,vi marks.txt

1)  Learnfk    Physics  80
2)  Toolfk   Maths    90
3)  Chromefk   Biology  87
4)  Poemfk   English  85
5)  Nesfk    History  89

  Let's take a look at the content first ：

  We try to use awk sentence , stay marks.txt Add a sentence before the text "This is the title."

awk 'BEGIN{printf "This is the title.\n"} {print}' marks.txt

This sentence is actually printed in front of the text , explain BEGIN Is the first execution , And only once

4. No, BEGIN The sentence of

We can execute repeated statements directly

awk '{print}' marks.txt

5. Write command to script

vi command.awk

And then use awk -f command.awk marks.txt perform

The effect is the same as direct execution .

6. Command specifies the variable

Use -v Variable can be specified , for example

awk -v name=Bob 'BEGIN{printf "hello, %s\n", name}{print}' marks.txt

  We can use it directly awk The specified variable .