a grep command and redirection to copy only the lines that have valid email addresses from one file to a new file. A valid email address is the one that is in the @

- is a sequence of letters and digits, and '.', '-' and '_' can appear between them. It must start with a letter or a digit, not with other characters.

Examples of valid users: 0223, "Tom", "tom09", "j.smith", "j_smith", "j-smith".

- is a sequence of at least two words, separated by character '.'. Each word is sequence of letters and can have character '-' between the letters.

Examples of valid hosts: "sg.se", "my-cs.com", ", "mail.un.org".