mh-format

MH-FORMAT(5)                        [nmh-1.5]                       MH-FORMAT(5)



NAME
       mh-format - format file for nmh message system

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

       There are a few alternate scan listing formats available in
       nmh/etc/scan.time, nmh/etc/scan.size, and nmh/etc/scan.timely.  Look in
       nmh/etc 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.


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

       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.  Some commands
       (such as ap and mhl) use a special component `%{text}' to refer to the
       text being processed; see their respective man pages for details and
       examples.

       A function escape is specified as `%(function)'.  All functions are
       built-in, and most have a string or numeric value.  A function escape may
       have an argument.  The argument follows the function escape: separating
       whitespace is discarded: `%(function argument)'.

       In addition to literal numbers or strings, the argument to a function
       escape can be another function, a component, or a control escape.  When
       the argument is a function or a component, they are listed without a
       leading `%'.  When control escapes are used as function arguments, they
       written as normally, with a leading `%';


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

            %< condition format-text
            %? condition format-text
                ...
            %| format-text
            %>

       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-texts is interpreted.  In other words,
       `%<' is like the "if", `%?' is like the "elseif", `%|' is like "else",
       and `%>' is like "endif".

       A `%<' or `%?' control escape causes its condition to be evaluated.  This
       condition is a component or function.  For integer valued functions or
       components, the condition is true if the function return or component
       value is non-zero, and false if zero.  For string valued functions or
       components, the condition is true if the function return or component
       value is a non-empty string, and false for an empty string.


       The `%?' control escape is optional, and may there may be more than one
       `%?' control escape in a conditional block.  The `%|' control escape is
       also optional, but may be included at most once.


   Function escapes
       Functions expecting an argument generally require an argument of a
       particular type.  In addition to the number and string types, these
       include:

            Argument Description            Example Syntax
            literal  A literal number       %(func 1234)
                     or string              %(func text string)
            comp     Any component          %(func{in-reply-to})
            date     A date component       %(func{date})
            addr     An address component   %(func{from})
            expr     Nothing                %(func)
                     or a subexpression     %(func(func2))
                     or control escape      %(func %<{reply-to}%|%{from}%>)

       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.

       Most arguments not of type expr are required.  When escapes are nested
       (via expr arguments), evaluation is done from inner-most to outer-most.
       As noted above, for the expr argument type, functions and components are
       written without a leading `%'.  Control escape arguments must use a
       leading `%', preceded by a space.

       For example,

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

       writes  the  value of the header component “From:” to the internal
       register named str; then (mymbox) reads str and writes its result to the
       internal register named 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:”.

   Evaluation
       The evaluation of format strings is performed by a small virtual machine.
       The machine is capable of evaluating nested expressions as described
       above, and in addition has an integer register num, and a text string
       register str.  When a function escape that accepts an optional argument
       is processed, and the argument is not present, the current value of
       either num or str is used as the argument: which register is used depends
       on the function, as listed below.

       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, setting num
       to 1 if the last explicit condition evaluated by a `%<' or `%?' control
       succeeded, and 0 otherwise.

       All component escapes, and those function escapes which return an integer
       or string value, evaluate to their value as well as setting str or num.
       Outermost escape expressions in these forms will print their value, but
       outermost escapes which return a boolean value do not result in printed
       output.

   Functions
       The function escapes may be roughly grouped into a few categories.

            Function    Argument   Result Description
            msg                  integer  message number
            cur                  integer  message is current (0 or 1)
            unseen               integer  message is unseen (0 or 1)
            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 (username)
            myhost               string   the user's local hostname
            myname               string   the user's name
            localmbox            string   the complete local 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.
            num                  integer  Set num to zero.
            lit         literal  string   Set str to arg.
            lit                  string   Clear str.
            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 (MIME-encoded)
                                          component
            unquote     expr     string   remove RFC-2822 quotes from str
            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
            putlit      expr              print str without space compression
            nodate      string   integer  Argument not a date string (0 or 1)
            formataddr  expr              append arg to str as a
                                          (comma separated) address list
            concataddr  expr              append arg to str as a
                                          (comma separated) address list,
                                          including duplicates,
                                          see Special Handling
            putaddr     literal           print str address list with
                                          arg as optional label;
                                          get line width from num

       The (me) function returns the username of the current user.  The (myhost)
       function returns the localname entry in mts.conf, or the local hostname
       if localname is not configured.  The (myname) function will return the
       value of the SIGNATURE environment variable if set, otherwise will return
       the passwd GECOS field (truncated at the first comma if it contains one)
       for the current user.  The (localmbox) function will return the complete
       form of the local mailbox, suitable for use in a “From” header.  It will
       return the “Local-Mailbox” profile entry if it is set; if it is not, it
       will be equivalent to:

            %(myname) <%(me)@%(myhost)>

       The following 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?
                                          (1=explicit,0=implicit,-1=unknown)
            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?
                                          (1=explicit,0=implicit,-1=unknown)
            date2local  date              coerce date to local timezone
            date2gmt    date              coerce date to GMT
            dst         date     integer  daylight savings in effect? (0 or 1)
            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

       These functions require an address component as an argument.  The return
       value of functions noted with `*' is computed from 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  List has the user's address? (0 or 1)
            host        addr     string   the host domain*
            nohost      addr     integer  no host was present (0 or 1)*
            type        addr     integer  host type* (0=local,1=network,
                                          -1=uucp,2=unknown)
            path        addr     string   any leading host route*
            ingrp       addr     integer  address was inside a group (0 or 1)*
            gname       addr     string   name of group*

       (A clarification on (mymbox{comp}) is in order.  This function 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 case.)

   Formatting
       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.

       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) are somewhat special: they print their result in the minimum
       number of characters required, and ignore any leading field width
       argument.  The (putlit) function outputs the exact contents of str
       register without any changes such as duplicate space removal or control
       character conversion.

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

   Special Handling
       A few functions have different behavior depending on what command they
       are being invoked from.

       In repl the (formataddr) function stores all email addresses encountered
       into an internal cache and will use this cache to suppress duplicate
       addresses.  If you need to create an address list that includes
       previously-seen addresses you may use the (concataddr) function, which is
       identical to (formataddr) in all other respects.  Note that (concataddr)
       will NOT add addresses to the duplicate-suppression cache.

   Other Hints and Tips
       Sometimes to format function writers it is confusing as to why output is
       duplicated.  The general rule to remember is simple: If a function or
       component escape is used where it starts with a %, then it will generate
       text in the output file.  Otherwise, it will not.

       A good example is a simple attempt to generate a To: header based on the
       From: and Reply-To: headers:

            %(formataddr %<{reply-to}%|%{from})%(putaddr To: )

       Unfortuantely if the Reply-to: header is NOT present, the output line
       that is generated will be something like:

            My From User <from@example.com>To: My From User <from@example.com>

       What went wrong?  When performing the test for the if clause (%<), the
       component is not output because it is considered an argument to the if
       statement (hence the rule about the lack of % applies).  But the
       component escape in our else statement (everything after the `%|') is NOT
       an argument to anything; the syntax is that it is written with a %, and
       thus the value of that component is output.  This also has the side
       effect of setting the str register, which is later picked up by the
       (formataddr) function and then output by (putaddr).  This format string
       has another bug as well; there should always be a valid width value in
       the num register when (putaddr) is called, otherwise bad formatting can
       take place.

       The solution is to use the (void) function; this will prevent the
       function or component from outputting any text.  With this in place (and
       using (width) to set the num register for the width, a better
       implementation would look like:

          %(formataddr %<{reply-to}%|%(void{from})%(void(width))%(putaddr To: )

       It should be noted here that the side-effects of functions and component
       escapes still are in force: as a result each component test in the
       if-elseif-else-endif clause sets the str register.

       As an additional note, the (formataddr) and (concataddr) functions have
       some behavior when it comes to the str register.  The starting point of
       the register is saved and is used to build up entries in the address
       list.

       You will find the ap and fmtdump utilities invaluable in debugging
       problems with format strings.

   Examples
       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; 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:

              %02(mon{date})/%02(mday{date})

       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,

            %<(mymbox{from})%<{to}To:%14(decode(friendly{to}))%>%>

       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; any MIME-encoded characters are decoded into the actual
       characters.  Continuing,

            %<(zero)%17(decode(friendly{from}))%>

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

            %(decode{subject})%<{body}<<%{body}>>%>

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

       For a more complicated example, next consider a possible 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.

            %?{from}%?{sender}%?{return-path}%>)\

       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:”.

            %(lit)%(formataddr{to})%(formataddr{cc})%(formataddr(me))\

       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.

            %<{message-id}In-Reply-To: %{message-id}\n%>\
            %<{message-id}References: %<{references} %{references}%>\
            %{message-id}\n%>
            --------

       If a message-id component was present, an “In-Reply-To:” header is output
       including the message-id, followed by a “References:” header with
       references, if present, and the message-id.  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(message-id))  then
                 print (“In-reply-to: ”)
                 print (message-id.value)
                 print (“\n”)
            endif
            if (comp_exists(message-id)) then
                 print (“References: ”)
                 if (comp_exists(references)) then
                       print(references.value);
                 endif
                 print (message-id.value)
                 print (“\n”)
            endif

       One more example: Currently, nmh supports very large message numbers, and
       it is not uncommon for a folder to have far more than 10000 messages.
       Nontheless (as noted above) the various scan format strings are inherited
       from older MH versions, and are generally hard-coded to 4 digits of
       message number before formatting problems start to occur.  The nmh format
       strings can be modified to behave more sensibly with larger message
       numbers:

              %(void(msg))%<(gt 9999)%(msg)%|%4(msg)%>

       The current message number is placed in num.  (Note that (msg) is an int
       function, not a component.)  The (gt) conditional is used to test whether
       the message number has 5 or more digits.  If so, it is printed at full
       width: otherwise at 4 digits.

SEE ALSO
       scan(1), repl(1), ap(8), dp(8)


CONTEXT
       None



MH.6.8                            11 June 2012                      MH-FORMAT(5)