Shell programming (script) (variable)

Define variable naming ：

• Only English letters can be used for naming , Numbers and underscores , The first character cannot begin with a number .
• No spaces in between , You can use underscores  _.
• You can't use punctuation .
• Out of commission bash Keywords in （ You can use help Command to view reserved keywords ）.

  Using variables

#!/bin/bash
your="tome"
echo $your

A read-only variable

#!/bin/bash

myUrl="https://www.google.com"
readonly myUrl
myUrl="https://www.runoob.com"

Delete variables

#!/bin/bash
your="tome"
echo $your
your="alibaba"
unset your
echo $your

Variable type

• local variable ： Local variables are defined in scripts or commands , At present only shell Valid in instance , other shell Started program cannot access local variables .
• environment variable ： All procedures , Include shell Program started , Can access environment variables , Some programs need environment variables to ensure their normal operation . When necessary shell Scripts can also define environment variables .
• shell Variable ：shell Variables are derived from shell Special variables for program settings .shell Some of the variables are environment variables , Some of them are local variables , These variables guarantee shell Normal operation of

shell character string