[系统运维]Linux 在工作中的实用命令

从文件中提取域名

# 以下是文件内容，
$ code cat ./test.txt
https://blog.csdn.net/weixin_44597836/article/details/106068197?utm_medium=distribute.pc_relevant.none-task-blog-2~default~baidujs_title~default-1.pc_relevant_paycolumn_v2&spm=1001.2101.3001.4242.2&utm_relevant_index=4
https://blog.csdn.net/hijiankang/article/details/70792456?spm=1001.2101.3001.6661.1&utm_medium=distribute.pc_relevant_t0.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-1.no_search_link&depth_1-utm_source=distribute.pc_relevant_t0.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-1.no_search_link&utm_relevant_index=1
https://www.baidu.com/s?ie=UTF-8&wd=uniq%20-c

http://www.baidu.com/s?ie=utf-8&f=3&rsv_bp=1&tn=baidu&wd=Linux%E7%BB%9F%E8%AE%A1%E7%94%A8%E6%88%B7%E7%99%BB%E5%BD%95%E6%AC%A1%E6%95%B0&oq=%25E7%25BB%259F%25E8%25AE%25A1%25E5%2590%258C%25E4%25B8%2580%25E4%25B8%25AA%25E7%2594%25A8%25E6%2588%25B7%25E6%259C%2580%25E8%25BF%2591%25E4%25B8%25A4%25E5%25A4%25A9%25E8%25AE%25BF%25E9%2597%25AEurl%25E6%25AC%25A1%25E6%2595%25B0&rsv_pq=bce1980e0003a02c&rsv_t=67c5aWCfrM%2BtOuxbLeC50dw1NA%2FCnHD91Tx3L%2FnTzFULOIt0tEzfWBbHxaQ&rqlang=cn&rsv_enter=1&rsv_dl=ts_7&rsv_sug3=30&rsv_sug1=14&rsv_sug7=101&rsv_sug2=1&rsv_btype=t&prefixsug=linux%2520%25E7%25BB%259F%25E8%25AE%25A1%25E7%2594%25A8%25E6%2588%25B7&rsp=7&inputT=39880&rsv_sug4=40171

https://zhuanlan.zhihu.com/p/52829308
https://zhuanlan.zhihu.com/p/52829308
https://blog.csdn.net/weixin_32161925/article/details/116838282
https://zhuanlan.zhihu.com/p/52829308
https://blog.csdn.net/weixin_32161925/article/details/116838282

# 一点一点地解读
# grep -o 指的是精准提取（只提取关键词，常用于正则），grep会把整行都显示出来
# http 完全匹配字符串"http"
# .\?   其中.值的是匹配s，可以有s，也可以没有，即s出现1次或0次，\? 指的是匹配0次或1次，必须用\进行转译
# :// 完全匹配字符串"://"
# .* 
# \. 完全匹配字符"."
# \w\+  其中\w 匹配大小写字母，下划线和数字，等价于 [a-zA-Z0-9_]，+匹配多次。
# \/ 指匹配/，必须匹配，不然有两条匹配不到
$ grep -o 'http.\?://.*\.\w\+\/' ./test.txt
https://blog.csdn.net/
https://blog.csdn.net/
https://www.baidu.com/
http://www.baidu.com/
https://zhuanlan.zhihu.com/
https://zhuanlan.zhihu.com/
https://blog.csdn.net/
https://zhuanlan.zhihu.com/
https://blog.csdn.net/