обрабатывать сообщения (process messages)
Выходные файлы (Output files)
Various mailx commands and command escapes can create or add to
files, including the mbox, the dead-letter file, and secondary
mailboxes. When mailx is used as described in this volume of
POSIX.1‐2017, these files shall be text files, formatted as
follows:
line beginning with From<space>
[one or more header-lines; see Commands in mailx]
empty line
[zero or more body lines
empty line]
[line beginning with From<space>...]
where each message begins with the From <space> line shown,
preceded by the beginning of the file or an empty line. (The
From <space> line is considered to be part of the message header,
but not one of the header-lines referred to in Commands in mailx;
thus, it shall not be affected by the discard, ignore, or retain
commands.) The formats of the remainder of the From <space> line
and any additional header lines are unspecified, except that none
shall be empty. The format of a message body line is also
unspecified, except that no line following an empty line shall
start with From <space>; mailx shall modify any such user-entered
message body lines (following an empty line and beginning with
From <space>) by adding one or more characters to precede the
'F'; it may add these characters to From <space> lines that are
not preceded by an empty line.
When a message from the system mailbox or entered by the user is
not a text file, it is implementation-defined how such a message
is stored in files written by mailx.
