command grep - JohnHau/mis GitHub Wiki
https://www.runoob.com/linux/linux-comm-grep.html
https://www.cyberciti.biz/faq/howto-use-grep-command-in-linux-unix/
https://man7.org/linux/man-pages/man1/grep.1.html
https://blog.gtwang.org/linux/linux-grep-command-tutorial-examples/
https://www.geeksforgeeks.org/grep-command-in-unixlinux/
https://phoenixnap.com/kb/grep-command-linux-unix-examples
https://wangchujiang.com/linux-command/c/grep.html
https://www.howtogeek.com/496056/how-to-use-the-grep-command-on-linux/
https://opensource.com/article/21/3/grep-cheat-sheet
https://www.cnblogs.com/ggjucheng/archive/2013/01/13/2856896.html
https://linuxhint.com/grep_command_linux/
https://linuxize.com/post/how-to-use-grep-command-to-search-files-in-linux/
https://swcarpentry.github.io/shell-novice/07-find/index.html
https://study.com/academy/lesson/regular-expressions-the-grep-command-in-linux.html
https://docs.rackspace.com/support/how-to/use-the-linux-grep-command/
https://support.infogix.com/hc/en-us/articles/360041952693-GREP-Command-in-Linux
https://www.javatpoint.com/linux-grep
https://tldp.org/LDP/Bash-Beginners-Guide/html/sect_04_02.html
https://www.hostinger.com/tutorials/grep-command-in-linux-useful-examples/
https://linux.die.net/man/1/grep
https://docs.oracle.com/cd/E19504-01/802-5826/6i9iclf5k/index.html
https://www.howtoforge.com/tutorial/linux-grep-command/
https://www.makeuseof.com/grep-command-practical-examples/
https://en.wikibooks.org/wiki/Grep