test.sh:
#!/bin/bash myUrl="http://www.google.com" readonly myUrl myUrl="http://www.runoob.com"
输出
bogon:Desktop macname$ ./test.sh ./test.sh: line 4: myUrl: readonly variable
参考：
https://www.runoob.com/linux/linux-shell-variable.html
原文：https://www.cnblogs.com/sea-stream/p/11403088.html