Seven. Shell script programming

Shell login mode, shell arithmetic operation, Shell logic operation, shell condition test, Shell selection statement

Shell programming in the first line indicates the path of the shell type to be executed

e.g #/bin/bash

1. Shell Login Method

Interactive login:/etc/profile--/etc/profile.d/*.sh--/~/.bahsh_profile--~/.BASHRC--/ETC/BASHRC

Non-interactive login: ~/.BASHRC--/ETC/BASHRC--/etc/profile.d/*.sh

2. Shell arithmetic operations

(1) Operation symbol:

+ Add

-Sub

* Mul

/div

% remainder

(2) Four ways to implement arithmetic operations

A. Let varname=expression

Let varname=2+3, let varname=2*3

B. varname=$[expression]

VARNAME=$[5*6]

C. varname=$ ((expression))

varname=$ ((2+3))

D. varname=$ (expr arg1 arg2 arg3 ...)

varname=$ (expr 2 + 3)

3. Logical operation

&& Logical AND

|| Logical OR

！ Logical not

4. Condition Testing

Determines whether an expression is true, completed by a test statement

Test command

Test EXPRESSION

[EXPRESSION]

[[EXPRESSION]]

Test comparison symbols

Numerical

-GT great than

-lt less than

-eq equal

-ne Not Equal

-ge great than or equal

-le less than or equal

e.g Test 2-eq 2, [4-ge 3]

String

= = Strings is equal

> Strings is great

< strings is less

! = strings is not equal

-Z "string": test whether the string is empty, the vacancy is true

-N "string": test whether the string is not empty, not empty is true

File test

TEST-E file test files are present

5. SELECT statement

If-then

If COMMAND

Then

COMMAND

If-then-else

If COMMAND

Then

COMMAND

If-then-elif-then-else

If COMMAND

Then

COMMAND

Elif

Then

COMMAND

...

Else

COMAND

Seven. Shell script programming