Provided by: nmh_1.7.1-4_amd64 bug

NAME

       mh-format - formatting language 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 to generate its  listing  of  messages;
       repl uses a format file to generate message replies, and so on.

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

       You  can  have your local nmh expert write new format commands or modify existing ones, or
       you can try your hand at it yourself.  This manual section explains how to do that.  Note:
       some familiarity with the C printf routine is assumed.

       A  format  string consists of ordinary text combined with 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 `%%'.

   SYNTAX
       Format  strings  are  built  around  escape  sequences.   There  are three types of escape
       sequence: 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.

   Component escapes
       A component escape is specified as `%{component}', and  exists  for  each  header  in  the
       message  being  processed.   For  example,  `%{date}'  refers  to the “Date:” field of the
       message.  All component escapes have a string value.  Such values are  usually  compressed
       by  converting  any  control characters (tab and newline included) to spaces, then eliding
       any leading or multiple spaces.  Some commands,  however,  may  interpret  some  component
       escapes  differently;  be  sure to refer to each command's manual entry for details.  Some
       commands (such as ap(8) and mhl(1)) use a special component `%{text}' to refer to the text
       being processed; see their respective man pages for details and examples.

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

            %(function argument)

       In addition to literal numbers or strings, the  argument  to  a  function  escape  can  be
       another function, or a component, or a control escape.  When the argument is a function or
       a component, the argument is specified without a leading `%'.   When  the  argument  is  a
       control escape, it is specified 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, which may be nested
       without ambiguity, 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 components and  functions  whose  value  is  an  integer,  the
       condition  is  true  if  it  is non-zero, and false if zero.  For components and functions
       whose value is a string, the condition is true it is a non-empty string, and false  if  an
       empty string.

       The  `%?'  control  escape  is  optional,  and can be used multiple times in a conditional
       block.  The `%|' control escape is also optional, but may only be used once.

   Function escapes
       Functions expecting an argument generally require an argument of a  particular  type.   In
       addition to the integer 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  date  and  addr types have the same syntax as the component type, comp, but require a
       header component which is a date, or address, string, respectively.

       Most arguments not of  type  expr  are  required.   When  escapes  are  nested  (via  expr
       arguments),  evaluation is done from innermost to outermost.  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 substituted as  the  argument:  the  register  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 escape 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 Return   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
            multiply    literal  integer  num multiplied by arg
            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 whitespace from str
            kilo        expr     string   express in SI units: 15.9K, 2.3M, etc.
                                          %(kilo) scales by factors of 1000,
            kibi        expr     string   express in IEC units: 15.5Ki, 2.2Mi.
                                          %(kibi) scales by factors of 1024.
            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 it 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 there is one; if 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 minutes
            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 RFC 822 rendering
            pretty      date     string   user-friendly rendering
            nodate      date     integer  returns 1 if date is invalid

       The  following 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 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)
            getmymbox   addr     string   the user's (first) address,
                                          with personal name
            getmyaddr   addr     string   the user's (first) address,
                                          without personal name
            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 printed
       immediately, 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.  Using a negative  value  for  the  field
       width  causes  right-justification  within  the  field, with padding on the left up to the
       field width.  Padding is with spaces except for  a  left-padded  putnumf  when  the  width
       starts  with  zero.   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.
       Similarly,  the  (zputlit)  function  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 to their default setting.  These terminal escapes 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  exceeding  this
       width will be truncated.  The one exception to this is that (zputlit) functions will still
       be executed if a terminal reset code is being placed at the end of a line.

   Special Handling
       Some functions have different behavior depending on the command they are 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) does not add addresses to the duplicate-suppression cache.

   Other Hints and Tips
       Sometimes, the writer of a format function is confused because output is duplicated.   The
       general  rule  to remember is simple: If a function or component escape begins with a `%',
       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: )

       Unfortunately,  if  the Reply-to: header is not present, the output line 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 (so the rule about not
       starting with % applies).  But the component escape  in  our  else  statement  (everything
       after  the `%|') is not an argument to anything; it begins 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).  The
       example format string above has another bug: 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 function and component escapes are still
       in force and, 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 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(1)  utility  invaluable  when debugging problems with format
       strings.

   Examples
       With all the above in mind, here is a breakdown of the default  format  string  for  scan.
       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 is present it is printed, followed by  a  space;  otherwise  a  `*'  is
       printed.  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, 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.  Nonetheless (as noted above)
       the various scan format strings, inherited from older MH  versions,  are  generally  hard-
       coded  to 4 digits for the message number. Thereafter, formatting problems 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 a function escape  which
       returns  an integer, it is 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), fmttest(1),

CONTEXT

       None