todo

[find] Run and understand. Find a string in a file with the find command

[sed] Run and understand. Add a newline to a target file using the sed command

[source] Run and understand. Execute different name with alias

[grep] Run and understand. Branching with the grep command

[grep] Run and understand. Get the line number of the relevant string using the grep command

[alias] Run and understand. Execute a command with any name using the alias command

[chgrp] Run and understand: Change the group name of a file with the chgrp command