declare的法;
定义环境变量:declare -x 变量名
修改环境变量为本地变量: declare +x 环境变量名
使变量变为可读:declare -r 变量名
[root@localhost opt]# bb=10
[root@localhost opt]# declare -r bb //把变量变为可读(不能修改和删除)
[root@localhost opt]# bb=20
bash: bb: readonly variable
[root@localhost opt]# unset bb
bash: unset: bb: cannot unset: readonly variable
[root@localhost opt]#
使变量变为可读的另一种方法: readonly 变量名
[root@localhost opt]# cc=20
[root@localhost opt]# readonly cc
[root@localhost opt]# cc=30
bash: cc: readonly variable
[root@localhost opt]# unset cc
bash: unset: cc: cannot unset: readonly variable
[root@localhost opt]#