Provided by: nmh_1.6-8build1_amd64 bug


       mh-format - format file for nmh message system


       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. A literal `%' can be inserted into a format
       file by using the sequence `%%'.

       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:”.

       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

       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.

       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  column width of terminal
            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
            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)
            unquote     expr     string   remove RFC 2822 quotes from str
            trim        expr              trim trailing whitespace 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
            zputlit     expr              print str without space compression;
                                          str must occupy no width on display
            bold                 string   set terminal bold mode
            underline            string   set terminal underlined mode
            standout             string   set terminal standout mode
            resetterm            string   reset all terminal attributes
            hascolor             boolean  terminal supports color
            fgcolor     literal  string   set terminal foreground color
            bgcolor     literal  string   set terminal background color
            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?
            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? (0 or 1)
            clock       date     integer  seconds since the UNIX epoch
            rclock      date     integer  seconds prior to current time
            tws         date     string   official RFC 822 rendering
            pretty      date     string   user-friendly rendering
            nodate      date     integer  returns 1 if date is invalid

       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

            Function    Argument Return   Description
            proper      addr     string   official RFC 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,
            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.)

       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 the str
       register  without  any  changes  such  as  duplicate  space  removal  or control character
       conversion.  The (zputlit) function similarly  outputs  the  exact  contents  of  the  str
       register,  but requires that those contents not occupy any output width.  It can therefore
       be used for outputting terminal escape sequences.

       There are a limited number of function escapes to output terminal escape sequences.  These
       sequences  are  retrieved  from the terminfo(5) database according to the current terminal
       setting.  The (bold), (underline), and (standout) escapes set bold mode,  underline  mode,
       and standout mode respectively.

       (hascolor) can be used to determine if the current terminal supports color.  (fgcolor) and
       (bgcolor) set the foreground and background colors respectively.  Both  of  these  escapes
       take one literal argument, the color name, which can be one of: black, red, green, yellow,
       blue, magenta, cyan, white.  (resetterm) resets all  terminal  attributes  back  to  their
       default setting.

       All  of  these terminal escape should be used in conjunction with (zputlit) (preferred) or
       (putlit), as the normal (putstr) function will strip out control characters.

       The available output width is kept in an internal register; any  output  past  this  width
       will  be  truncated.   The  one  exception  to  this  is (zputlit) functions will still be
       executed in case a terminal reset code is being placed at the end of the line.

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

       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 <>To: My From User <>

       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

       As  an  additional note, the (formataddr) and (concataddr) functions have special 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 fmttest utility invaluable when debugging problems with format strings.

       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:


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


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


       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.


       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.

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

       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

            if (comp_exists(message-id))  then
                 print (“In-reply-to: ”)
                 print (message-id.value)
                 print (“\n”)
            if (comp_exists(message-id)) then
                 print (“References: ”)
                 if (comp_exists(references)) then
                 print (message-id.value)
                 print (“\n”)

       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.


       scan(1), repl(1), fmttest(1),