The valid command characters are: B - Backup, type the previous message C - Current message, give current message number and the file name D - Delete, mark a message sequence for deletion E - Exit, exit and update the open file G - Goto, changes the current message number H - Headers, print the headers of a message sequence L - List, provide a listing of a message sequence M - Move, move a sequence into another file and then delete it N - Next, type the next message O - Overwrite, remove all deleted messages from the file P - Put, move a message sequence into another file Q - Quit, leave the msg program R - Read, open and read another file T - Type, output a message sequence to the console U - Undelete, remove the deletion mark from a message sequence Single quote(') - Mark a message sequence as 'examined' Minus sign(-) - Mark a message sequence as 'not examined' A message sequence is composed of: 1) any single number or 2) any two numbers separated by any nonnumeric character or 3) one of the following special sequence characters: A - All messages D - Deleted messages E - Examined messages I - All messages in inverse order N - Not examined messages U - Undeleted messages