Shell's declare defining variables

Experimental environment

Command description

The declare and typeset commands are bash's built-in commands (BUILTIN commands), both of which function exactly the same way to set variable values and properties.
Typeset is now deprecated and replaced by declare to see the Help manual:

~]# help typesettypeset: typeset [-aAfFgilrtux] [-p] name[=value] ...    Set variable values and attributes.        Obsolete.  See `help declare‘.

~]# help declaredeclare: declare [-aAfFgilrtux] [-p] [name[=value] ...]    Set variable values and attributes.

Command options

The option parameters for typeset and declare are generic and are described below with declare:

Declare variables and give them attributes. If no NAMEs is given, display the attributes and values of all variables.
declare [-aaffgilrtux] [-P] [Name[=value] ...]

Options:

-f [name]：列出之前由用户在脚本中定义的函数名称和函数体；-F [name]：仅列出自定义函数名称；-g name：在shell函数中可创建全局变量；-p [name]：显示指定变量的属性和值；-a name：声明变量为普通数组；-A name：声明变量为关联数组（支持索引下标为字符串）；-i name ：将变量定义为整数型（求值结果仅为整数，否则显示为0）；-r [name[=value]] 或 readonly name：将变量定义为只读（不可修改和删除）；-x name[=value] 或 export name[=value]：将变量设置为环境变量；

PS: Use + to cancel the definition of a variable type, such as canceling an integer variable definition declare +i name.

Unset Name: Cancels the property and value of the variable, except for the read-only variable.
Unset values and attributes of shell variables and functions.

Using the example

#!/bin/bashecho "Set a custom Function-func1" echofunc1 () {echo this is a function.} echo "Lists the function body." echo "=============================" Declare-f echoecho "Lists the function name." echo "=============================" Declare-f echodeclare-i var1 # var1 are an Integer.var1=2367echo "var1 declar Ed as $var 1 "var1=var1+1 # Integer declaration eliminates the need for ' let '. echo" Var1 incremented by 1 is $var 1. " # Attempt to change variable declared as Integer.echo "attempting to change var1 to floating point value, 2367.1." var1=2367.1 # Results in error message, with the change to Variable.echo "Var1 is still $var 1" echodeclare-r var2=13.  # ' Declare ' permits setting a variable property #+ and simultaneously assigning it A Value.echo "Var2 declared as $var 2" # Attempt to change readonly Variable.echoecho "Change the var2 's values to 13.37" V AR2=13.37 # generates error message, and exit from SCript.echo "Var2 is still $var 2" # This line would not Execute.exit 0 # Script won't exit here .

Reference links

Declare Advanced bash-scripting Guide

Shell's declare defining variables