oper [<nick> [<password>]]

The OPER command is used to gain irc operator status on the current server, with the stipulation that the specified (or current) nickname and password match an O: line entry in the server's configuration. If a password is not specified, the client will prompt for one.

Unlike DEOP, the MODE command cannot be used to gain operator status.

Specifying the password on the input line is not recommended, for many reasons, the most obvious being that anyone with a line of sight to your monitor can see what your password is. When the client prompts for a password, it does not display it as it is typed. Further, the client's command history may be written to a file, which would compromise the password if the history file is world-readable.