Specify the variable type: declare or typeset

Specify the type of the variable: Use the declare or typeset declare/typeset option-r read-only declare-r var1 (declare-r var1 and readonly var1 are exactly the same) this is the same as the const keyword in C language. It is used to specify the variable as read-only. if you try to modify the value of a read-only variable, an error message is generated. root @ ubuntu :~ /Resource/shell-study/0508-2013 # declare-r var1 = 11 root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ var1 11 root @ ubuntu :~ /Resource/shell-study/0508-2013 # let "var1 = 12" bash: var1: readonly variable root @ ubuntu :~ /Resource/shell-study/0508-2013 # ^ C root @ ubuntu :~ /Resource/shell-study/0508-2013 # readonly var2 = 12 root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ var2 12 root @ ubuntu :~ /Resource/shell-study/0508-2013 # let "var2 = 13" bash: var2: readonly variable root @ ubuntu :~ /Resource/shell-study/0508-2013 #-I integer declare-I number script will process the variable "number" according to the integer type. if you specify a variable as an integer, specific arithmetic operations are allowed even if there is no expr or let Command. #! /Bin/bash declare-I number = 3 echo "number = $ number" number = "123" echo "number = $ number" number = "abc" echo "number = $ number "number = 6/3 echo" number = $ number "not_int_number = 6/3 echo" not_int_number = $ not_int_number "exit 0 check the result: root @ ubuntu :~ /Resource/shell-study/0508-2013 #./test1.sh number = 3 number = 123 number = 0 number = 2 not_int_number = 6/3 root @ ubuntu :~ /Resource/shell-study/0508-2013 #-a array declare-a indices variable indices will be treated as an array. root @ ubuntu :~ /Resource/shell-study/0508-2013 # declare-a str root @ ubuntu :~ /Resource/shell-study/0508-2013 # str = (1 2 3 4 5) root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ str 1 root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ {str [0]} 1 root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ {str [1]} 2 root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ {str [2]} 3 root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ {str [3]} 4 root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ {str [4]} 5 root @ ubuntu :~ /Resource/shell-study/0508-2013 # use $ {array name [subscript]} To subscript from 0: * or @ to get the entire array content, the array name [subscript] can be used to reference and assign values to it. If the subscript does not exist, a new array element is automatically added. The corresponding elements can be cleared directly through the unset array [subscript, clear the entire data root @ ubuntu: ~ Without subscript :~ /Resource/shell-study/0508-2013 # str = (1 2 3 4 5) root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ str 1 root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ {str [*]} 1 2 3 4 5 root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ {str [@]} 1 2 3 4 5 root @ ubuntu :~ /Resource/shell-study/0508-2013 # str [1] = 10 root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ {str [@]} 1 10 3 4 5 root @ ubuntu :~ /Resource/shell-study/0508-2013 # unset str root @ ubuntu :~ /Resource/shell-study/0508-2013 # echo $ {str [@]} root @ ubuntu :~ /Resource/shell-study/0508-2013 #-f function declare-f if declare-f is used in the script without adding any parameters, all functions previously defined in this script will be listed. declare-f function_name if declare-f function_name is used in the script, only the name of this function will be listed. root @ ubuntu :~ /Resource/shell-study/0508-2013 # declare-f command_not_found_handle () {if [-x/usr/lib/command-not-found]; then/usr/bin/python/usr/lib/command-not-found -- $1; return $ ?; Else if [-x/usr/share/command-not-found]; then/usr/bin/python/usr/share/command-not-found -- $1; return $ ?; Else return 127; fi} root @ ubuntu :~ /Resource/shell-study/0508-2013 # declare-f hello-x exportdeclare-x var3 will declare a variable and be exported as the environment variable of the script. -x var = $ valuedeclare-x var3 = 373declare command allows you to assign values to a variable while declaring the variable type.