Provided by: nmh_1.3-1_i386 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