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mh-format (5)
  • >> mh-format (5) ( Linux man: Форматы файлов )


    mh-format - format file for nmh message system


    some nmh commands  


    Several nmh commands utilize either a format string or a format file during their execution. For example, scan (1) uses a format string which directs it how to generate the scan listing for each message; repl (1) uses a format file which directs it how to generate the reply to a message, and so on.

    Format strings are designed to be efficiently parsed by nmh which means they are not necessarily simple to write and understand. This means that novice, casual, or even advanced users of nmh should not have to deal with them.

    There are a few alternate scan listing formats available in /etc/nmh/scan.time, /etc/nmh/scan.size, and /etc/nmh/scan.timely. Look in /etc/nmh for other scan and repl format files which may have been written at your site.

    It suffices to have your local nmh expert actually write new format commands or modify existing ones. This manual section explains how to do that. Note: familiarity with the C printf routine is assumed.

    A format string consists of ordinary text, and special multi-character escape sequences which begin with `%'. When specifying a format string, the usual C backslash characters are honored: `\b', `\f', `\n', `\r', and `\t'. Continuation lines in format files end with `\' followed by the newline character.

    There are three types of escape sequences: header components, built-in functions, and flow control.

    A component escape is specified as `%{component}', and exists for each header found in the message being processed. For example `%{date}' refers to the ``Date:'' field of the appropriate message. All component escapes have a string value. Normally, component values are compressed by converting any control characters (tab and newline included) to spaces, then eliding any leading or multiple spaces. However, commands may give different interpretations to some component escapes; be sure to refer to each command's manual entry for complete details.

    A function escape is specified as `%(function)'. All functions are built-in, and most have a string or numeric value.

    A control escape is one of: `%<', `%?', `%|', or `%>'. These are combined into the conditional execution construct:

                    format text 1
                    format text 2
                    format text 3
                    format text N

    Extra white space is shown here only for clarity. These constructs may be nested without ambiguity. They form a general if-elseif-else-endif block where only one of the format text segments is interpreted.

    The `%<' and `%?' control escapes causes a condition to be evaluated. This condition may be either a component or a function. The four constructs have the following syntax:


    These control escapes test whether the function or component value is non-zero (for integer-valued escapes), or non-empty (for string-valued escapes).

    If this test evaulates true, then the format text up to the next corresponding control escape (one of `%|', `%?', or `%>') is interpreted normally. Next, all format text (if any) up to the corresponding `%>' control escape is skipped. The `%>' control escape is not interpreted; normal interpretation resumes after the `%>' escape.

    If the test evaluates false, however, then the format text up to the next corresponding control escape (again, one of `%|', `%?', or `%>') is skipped, instead of being interpreted. If the control escape encountered was `%?', then the condition associated with that control escape is evaluated, and interpretation proceeds after that test as described in the previous paragraph. If the control escape encountered was `%|', then the format text up to the corresponding `%>' escape is interpreted normally. As above, the `%>' escape is not interpreted and normal interpretation resumes after the `%>' escape.

    The `%?' control escape and its following format text is optional, and may be included zero or more times. The `%|' control escape and its following format text is also optional, and may be included zero or one times.

    Most functions expect an argument of a particular type:

    Argument Description            Example Syntax
    literal  A literal number,      %(func 1234)
             or string              %(func text string)
    comp     Any header component   %(func{in-reply-to})
    date     A date component       %(func{date})
    addr     An address component   %(func{from})
    expr     An optional component, %(func(func2))
             function or control,   %(func %<{reply-to}%|%{from}%>)
             perhaps nested         %(func(func2{comp}))

    The types date and addr have the same syntax as comp, but require that the header component be a date string, or address string, respectively.

    All arguments except those of type expr are required. For the expr argument type, the leading `%' must be omitted for component and function escape arguments, and must be present (with a leading space) for control escape arguments.

    The evaluation of format strings is based on a simple virtual machine with an integer register num, and a text string register str. When a function escape is processed, if it accepts an optional expr argument which is not present, it reads the current value of either num or str as appropriate.

    Component escapes write the value of their message header in str. Function escapes write their return value in num for functions returning integer or boolean values, and in str for functions returning string values. (The boolean type is a subset of integers with usual values 0=false and 1=true.) Control escapes return a boolean value, and set num.

    All component escapes, and those function escapes which return an integer or string value, pass this value back to their caller in addition to setting str or num. These escapes will print out this value unless called as part of an argument to another escape sequence. Escapes which return a boolean value do pass this value back to their caller in num, but will never print out the value.

    Function   Argument Return   Description
    msg                 integer  message number
    cur                 integer  message is current
    unseen              integer  message is unseen
    size                integer  size of message
    strlen              integer  length of str
    width               integer  output buffer size in bytes
    charleft            integer  bytes left in output buffer
    timenow             integer  seconds since the UNIX epoch
    me                  string   the user's mailbox
    eq         literal  boolean  num == arg
    ne         literal  boolean  num != arg
    gt         literal  boolean  num > arg
    match      literal  boolean  str contains arg
    amatch     literal  boolean  str starts with arg
    plus       literal  integer  arg plus num
    minus      literal  integer  arg minus num
    divide     literal  integer  num divided by arg
    modulo     literal  integer  num modulo arg
    num        literal  integer  Set num to arg
    lit        literal  string   Set str to arg
    getenv     literal  string   Set str to environment value of arg
    profile    literal  string   Set str to profile component arg value
    nonzero    expr     boolean  num is non-zero
    zero       expr     boolean  num is zero
    null       expr     boolean  str is empty
    nonnull    expr     boolean  str is non-empty
    void       expr              Set str or num
    comp       comp     string   Set str to component text
    compval    comp     integer  Set num to ``atoi(comp)''
    decode     expr     string   decode str as RFC-2047 component
    trim       expr              trim trailing white-space from str
    putstr     expr              print str
    putstrf    expr              print str in a fixed width
    putnum     expr              print num
    putnumf    expr              print num in a fixed width

    These functions require a date component as an argument:

    Function   Argument Return   Description
    sec        date     integer  seconds of the minute
    min        date     integer  minutes of the hour
    hour       date     integer  hours of the day (0-23)
    wday       date     integer  day of the week (Sun=0)
    day        date     string   day of the week (abbrev.)
    weekday    date     string   day of the week
    sday       date     integer  day of the week known?
    mday       date     integer  day of the month
    yday       date     integer  day of the year
    mon        date     integer  month of the year
    month      date     string   month of the year (abbrev.)
    lmonth     date     string   month of the year
    year       date     integer  year (may be > 100)
    zone       date     integer  timezone in hours
    tzone      date     string   timezone string
    szone      date     integer  timezone explicit?
    date2local date              coerce date to local timezone
    date2gmt   date              coerce date to GMT
    dst        date     integer  daylight savings in effect?
    clock      date     integer  seconds since the UNIX epoch
    rclock     date     integer  seconds prior to current time
    tws        date     string   official 822 rendering
    pretty     date     string   user-friendly rendering
    nodate     date     integer  str not a date string

    These functions require an address component as an argument. The return value of functions noted with `*' pertain only to the first address present in the header component.

    Function   Argument Return   Description
    proper     addr     string   official 822 rendering
    friendly   addr     string   user-friendly rendering
    addr       addr     string   mbox@host or host!mbox rendering*
    pers       addr     string   the personal name*
    note       addr     string   commentary text*
    mbox       addr     string   the local mailbox*
    mymbox     addr     integer  the user's addresses? (0=no,1=yes)
    host       addr     string   the host domain*
    nohost     addr     integer  no host was present*
    type       addr     integer  host type* (0=local,1=network,
    path       addr     string   any leading host route*
    ingrp      addr     integer  address was inside a group*
    gname      addr     string   name of group*
    formataddr expr              append arg to str as a
                                 (comma separated) address list
    putaddr    literal           print str address list with
                                 arg as optional label;
                                 get line width from num

    When escapes are nested, evaluation is done from inner-most to outer-most. The outer-most escape must begin with `%'; the inner escapes must not. For example,

          %<(mymbox{from}) To: %{to}%>

    writes the value of the header component ``From:'' to str; then (mymbox) reads str and writes its result to num; then the control escape evaluates num. If num is non-zero, the string ``To: '' is printed followed by the value of the header component ``To:''.

    A minor explanation of (mymbox{comp}) is in order. In general, it checks each of the addresses in the header component ``comp'' against the user's mailbox name and any Alternate-Mailboxes. It returns true if any address matches, however, it also returns true if the ``comp'' header is not present in the message. If needed, the (null) function can be used to explicitly test for this condition.

    When a function or component escape is interpreted and the result will be immediately printed, an optional field width can be specified to print the field in exactly a given number of characters. For example, a numeric escape like %4(size) will print at most 4 digits of the message size; overflow will be indicated by a `?' in the first position (like `?234'). A string escape like %4(me) will print the first 4 characters and truncate at the end. Short fields are padded at the right with the fill character (normally, a blank). If the field width argument begins with a leading zero, then the fill character is set to a zero.

    As above, the functions (putnumf) and (putstrf) print their result in exactly the number of characters specified by their leading field width argument. For example, %06(putnumf(size)) will print the message size in a field six characters wide filled with leading zeros; %14(putstrf{from}) will print the ``From:'' header component in fourteen characters with trailing spaces added as needed. For putstrf, using a negative value for the field width causes right-justification of the string within the field, with padding on the left up to the field width. The functions (putnum) and (putstr) print their result in the minimum number of characters required, and ignore any leading field width argument.

    The available output width is kept in an internal register; any output past this width will be truncated.

    Comments may be inserted in most places where a function argument is not expected. A comment begins with `%;' and ends with a (non-escaped) newline.

    With all this in mind, here's the default format string for scan. It's been divided into several pieces for readability. The first part is:

          %4(msg)%<(cur)+%| %>%<{replied}-%?{encrypted}E%| %>

    which says that the message number should be printed in four digits, if the message is the current message then a `+' else a space should be printed, and if a ``Replied:'' field is present then a `-' else if an ``Encrypted:'' field is present then an `E' otherwise a space should be printed. Next:


    the month and date are printed in two digits (zero filled) separated by a slash. Next,

          %<{date} %|*>

    If a ``Date:'' field was present, then a space is printed, otherwise a `*'. Next,


    if the message is from me, and there is a ``To:'' header, print `To:' followed by a ``user-friendly'' rendering of the first address in the ``To:'' field. Continuing,


    if either of the above two tests failed, then the ``From:'' address is printed in a ``user-friendly'' format. And finally,


    the subject and initial body (if any) are printed.

    For a more complicated example, next consider the default replcomps format file.

          %(lit)%(formataddr %<{reply-to}

    This clears str and formats the ``Reply-To:'' header if present. If not present, the else-if clause is executed.


    This formats the ``From:'', ``Sender:'' and ``Return-Path:'' headers, stopping as soon as one of them is present. Next:

          %<(nonnull)%(void(width))%(putaddr To: )\n%>\

    If the formataddr result is non-null, it is printed as an address (with line folding if needed) in a field width wide with a leading label of ``To: ''.


    str is cleared, and the ``To:'' and ``Cc:'' headers, along with the user's address (depending on what was specified with the ``-cc'' switch to repl) are formatted.

          %<(nonnull)%(void(width))%(putaddr cc: )\n%>\

    If the result is non-null, it is printed as above with a leading label of ``cc: ''.

          %<{fcc}Fcc: %{fcc}\n%>\

    If a ``-fcc folder'' switch was given to repl (see repl (1) for more details about %{fcc}), an ``Fcc:'' header is output.

          %<{subject}Subject: Re: %{subject}\n%>\

    If a subject component was present, a suitable reply subject is output.

         %<{date}In-reply-to: Your message of "\

    If a date component was present, an ``In-Reply-To:'' header is output with the preface ``Your message of ''. If the date was parseable, it is output in a user-friendly format, otherwise it is output as-is. The message-id is included if present. As with all plain-text, the row of dashes are output as-is.

    This last part is a good example for a little more elaboration. Here's that part again in pseudo-code:

    if (comp_exists(date))  then
         print (``In-reply-to: Your message of \``'')
         if (not_date_string(date.value) then
              print (date.value)
              print (pretty(date.value))
         print (``\'''')
         if (comp_exists(message-id)) then
              print (``\n\t'')
              print (message-id.value)
         print (``\n'')

    Although this seems complicated, in point of fact, this method is flexible enough to extract individual fields and print them in any format the user desires. None None scan(1), repl(1), ap(8), dp(8) None None




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