Bash Shell之declare定义变量
发布时间:2020-12-15 20:07:11 所属栏目:安全 来源:网络整理
导读:实验环境 ~]# cat /etc/redhat-release CentOS Linux release 7.3.1611 (Core) 命令说明 declare 与 typeset 命令都是bash的内建命令(builtin commands),两者所实现的功能完全一样,用来设置变量值和属性。 typeset现已弃用,由declare进行替代,可查看帮
实验环境~]# cat /etc/redhat-release CentOS Linux release 7.3.1611 (Core) 命令说明declare 与 typeset 命令都是bash的内建命令(builtin commands),两者所实现的功能完全一样,用来设置变量值和属性。 ~]# help typeset typeset: typeset [-aAfFgilrtux] [-p] name[=value] ... Set variable values and attributes. Obsolete. See `help declare'. ~]# help declare declare: declare [-aAfFgilrtux] [-p] [name[=value] ...] Set variable values and attributes. 命令选项typeset 和 declare的选项参数是通用的,下面以declare进行说明: Declare variables and give them attributes. If no NAMEs are given,display the attributes and values of all variables. declare [-aAfFgilrtux] [-p] [name[=value] ...] 选项:-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:使用 + 可取消定义的变量类型,如取消整数变量定义declare +i name。 unset name:取消已定义变量的属性和值,只读变量除外。 Unset values and attributes of shell variables and functions. 使用示例#!/bin/bash echo "Set a custom function - func1" echo func1 () { echo This is a function. } echo "Lists the function body." echo "=============================" declare -f echo echo "Lists the function name." echo "=============================" declare -F echo declare -i var1 # var1 is an integer. var1=2367 echo "var1 declared as $var1" var1=var1+1 # Integer declaration eliminates the need for 'let'. echo "var1 incremented by 1 is $var1." # 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 no change to variable. echo "var1 is still $var1" echo declare -r var2=13.36 # 'declare' permits setting a variable property #+ and simultaneously assigning it a value. echo "var2 declared as $var2" # Attempt to change readonly variable. echo echo "Change the var2's values to 13.37" var2=13.37 # Generates error message,and exit from script. echo "var2 is still $var2" # This line will not execute. exit 0 # Script will not exit here. 参考链接declare Advanced Bash-Scripting Guide (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |