在Linux bash shell中使用多个点的正则表达式给出了奇怪的结果

I tried to match a substring including a lot of dots, and it failed in Debian Linux shell. I made a simple script to look how dots are processed and found it completely out of rules. I retried it Bash, perl, Ubunta shell it all the same. The script and output are below. I tried to match a substring including a lot of