mail
命令手册The command operates on the user's mailbox if no argument is given. To send an email the message body is built from standard input.
mail --subject="{{subject line}}" {{to_user@example.com}}
mail --subject="{{$HOSTNAME filename.txt}}" {{to_user@example.com}} < {{path/to/filename.txt}}
tar cvzf - {{path/to/directory1 path/to/directory2}} | uuencode {{data.tar.gz}} | mail --subject="{{subject_line}}" {{to_user@example.com}}