Provided by: nmh_1.3-1build1_amd64 bug

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.

       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
            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
            nodate      string   integer  Argument not a date string (0 or 1)
            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

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

   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