Six. Bash script (bash scripts), bash variable

Shell variables, shell scripts basics

Shell variable Categories: environment variables, local variables, local variables, positional variables, special variables

1.shell Local Variables

(1) Assigning values to variables

Name= "Value"

Value

String Name= "string"

Variable reference name= "$name"

Command Reference name= ' command ', name=$

(2) Variable reference

$name,%{name}

"": if referenced, the variable reference is replaced with the value of the variable
': Strong reference, where the variable reference is not replaced with its variable value, keeping the original string
' Command ', $ (command): Commands reference

(3) Delete local variables

unset name

(4) Read-only variable, can not change its value after setting, can not be destroyed, only after the shell process ends its life

ReadOnly Name

Declare-r Name

2.shell Environment variables

(1) Assigning values to variables

Export Name=value

Declare-x Name=value

Local variable promoted to environment variable Expoert name, declaere-x name

(2) Display environment variables

Export

Env

Printenv

3. Deleting variables

unset name

4. Show all variables

Set:set or unset values of the shell options and positional parameters.

5. Position variables

Calling parameters passed to the script from the command line in the script

$, $ ... : corresponding to the command line of the 1th, 2nd ... A parameter

$: Command itself

$*: All parameters passed to the script, all parameters as a whole

[Email protected]: All parameters passed to the script, each parameter is independent

$#: Number of arguments passed in a script

Shift [n]: Kicks out n parameters

6. Logic operation:

&&: With

|| : OR

! : Non-

Short-circuit Operation:

A&&b: If A is false, B is not executed

a| | B: If True, the B is not executed

7. Shell programming Features: Process oriented (sequential execution, loop execution, select execution), interpreting execution

8. The first line of the script indicates the interpreter used to execute the script

#!/bin/bash
#!/usr/bin/python
#!/usr/bin/perl

9. Pstree:display a tree of process: show the tree of processes

Six. Bash script (bash scripts), bash variable