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The following ~ escapes are defined:
~?		Print this message
~~		Quote a single tilde
~.		Same as .
~A		Equivalent to: ~i Sign
~a		Equivalent to: ~i sign
~b users	Add users to "blind" cc list
~c users	Add users to cc list
~C		Dump core
~d		Read in dead.letter
~e		Edit the message buffer
~f messages	Read in messages
~F messages	Same as ~f, but keep all header lines
~h		Prompt for to list, subject and cc list
~i name		Insert the value of the named variable
~m messages	Read in messages, right shifted by a tab
~M messages	Same as ~m, but keep all header lines
~p		Print the message buffer
~q		Quit, save partial message in dead.letter
~r file		Read a file into the message buffer
~r !command	Insert the output of the command in the message
~< file		Same as ~r
~< !command	Same as ~r
~R address	Set reply-to
~s subject	Set subject
~t users	Add users to the To list
~v		Invoke display editor on message
~w file		Write message onto file.
~x		Quit, do not save to dead.letter
~?		Print this message
~! command	Invoke the shell
~| command	Pipe the message through the command
~^ command	Same as ~|
~_ mail-cmd	Perform the command-level request
~: mail-cmd	Same as ~_
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