Early preparation for big data on Shell basics

One: Regular expression

1. The difference between a wildcard and a regular expression

Wildcard characters *,? ，[]。

Difference:

Wildcard characters to match file names

The regular expression is to match the string

2. Meaning of ". *"

.: Any character

*: Matches the previous character any time

3. Filter out lines with a character

　　

4. Filter out lines without a keyword

　　

5. Show lines that begin with #

　　

6. Display lines that are not in English at the beginning

　　

7. Print o The row that appears two times

　　

8. Show 0 One or more characters appear

　　

9. Print lines that begin with R and end with N

　　

Two: Variables

1. View of environment variables

　　

2. Position variables

$1,$2,...... $9, respectively.

3. Pre-defined variables

　　

　　

4. Custom variables

Syntax format: name=[value]

Naming rules: Variable equals cannot have spaces on either side

Use export as a global variable

Called when using $.

Three: arithmetic operations

1. Syntax format

$ ((expression))

$[]

Expr

　　

Four: Built-in judgment

1. Test expressions

　　

　　

2. Numerical comparison

-eq

-ne

-gt

-ge

-lt

-le

3. String test

=

！ =

4. File Testing

-E: The file exists, it's true.

5. Logical operators

And! , or-O, not-a

6. Time

　　

7. Find out which package the command comes from

　　

V: Shell statement

1.for Control Statements

）

　　

）

　　

）

　　

）

　　

2.while Cycle

　　

　　

3 .....

。。。。。。

(The following will be completed next week)

Early preparation for big data on Shell basics