Provided by: nmh_1.8-1_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 or context
                                          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
            trimr       expr     string   Like %(trim), also returns string
            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.
            ordinal     expr     string   Output ordinal suffix based on value
                                          of num (st, nd, rd, th)
            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.)

       The  friendly{comp}) call will return any double-quoted “personal name” (that is, anything
       before <>), then it will return that.  If there's no personal name but there is  a  “note”
       (comments  string  after  an  email address), it will return that.  If there is neither of
       those it will just return the bare email address.

   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