Name mh-format - format file for nmh message system Synopsis some nmh commands 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. Format strings are designed to be efficiently parsed by nmh which means they are not necessarily simple to write and understand. This means that novice, casual, or even advanced users of nmh should not have to deal with them. There are a few alternate scan listing formats available in /etc/nmh/scan.time, /etc/nmh/scan.size, and /etc/nmh/scan.timely. Look in /etc/nmh 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 escapesequences 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 pro- cessed. 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 interpreta- tions 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 argu- ment follows the function escape: separating whitespace is discarded: `%(function argument)'. The argument to a function escape is processed in argument mode. A function or component escape evaluated in argu- ment mode should not be preceded by a leading `%'. Condi- tional escapes (see below) are allowed, and are entered normally. Control-flow escapes A control escape is one of: `%<', `%?', `%|', or `%>'. These are combined into the conditional execution con- struct: %< 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. A `%<' or `%?' control escape causes its condition to be evaluated. This condition is a component or function escape evaluated in argument mode. The control escape tests whether the function or component escape evaluates non-zero (for an integer-valued escape) or non-empty (for a string-valued escape). If the condition of a `%<' or `%?' control escape evaulates true, or a `%|' escape is encountered, then the format-text of that escape (up to the next corresponding `%|', `%?', or `%>' control escape) is interpreted nor- mally. Text up to the corresponding `%>' control escape is then skipped, and the `%>' control escape is discarded. If the condition of a `%<' or `%?' control escape evalu- ates false, however, the format-text (up to the next cor- responding `%|', `%?', or `%>' control escape) is skipped instead of being interpreted. Evaluation then continues at the new escape. The `%?' control escape is optional, and may be included zero or more times. The `%|' control escape is also optional, and may be included at most once. Function escapes Functions expecting an argument generally require an argu- ment 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, the evaluation is performed in argument mode: the leading `%' must be omitted for compo- nent and function escape arguments, and must be present (with a leading space) for control escape arguments. For example, %<(mymbox{from}) To: %{to}%> writes the value of the header component "From:" to str; then (mymbox) reads str and writes its result to 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 expres- sions 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 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 These 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 argu- ment. The return value of functions noted with `*' is computed from the first address present in the header com- ponent. Function Argument Return Description proper addr string official 822 rendering friendly addr string user-friendly rendering addr addr string mbox(_at_)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 compo- nent "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 charac- ter (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(put- numf(size)) will print the message size in a field six characters wide filled with leading zeros; %14(put- strf{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 func- tions (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 regis- ter; 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 read- ability. 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(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. Continuing, %<(zero)%17(friendly{from})%> if either of the above two tests failed, then the "From:" address is printed in a "user-friendly" format. And finally, %{subject}%<{body}<<%{body}%> the subject and initial body (if any) are printed. For a more complicated example, next consider the default replcomps format file. %(lit)%(formataddr %<{reply-to} This clears str and formats the "Reply-To:" header if pre- sent. 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 sub- ject is output. %<{date}In-reply-to: Your message of "\ %<(nodate{date})%{date}%|%(pretty{date})%>."%<{message-id} %{message-id}%>\n%>\ -------- If a date component was present, an "In-Reply-To:" header is output with the preface "Your message of ". If the date was parseable, it is output in a user-friendly for- mat, otherwise it is output as-is. The message-id is included if present. As with all plain-text, the row of dashes are output as-is. This last part is a good example for a little more elabo- ration. Here's that part again in pseudo-code: if (comp_exists(date)) then print ("In-reply-to: Your message of \"") if (not_date_string(date.value) then print (date.value) else print (pretty(date.value)) endif print ("\"") if (comp_exists(message-id)) then print ("\n\t") print (message-id.value) endif print ("\n") endif One more example: Currently, nmh supports very large mes- sage 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 sen- sibly 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) con- ditional is used to test whether the message number has 5 or more digits. If so, it is printed at full width: oth- erwise at 4 digits. See Also scan(1), repl(1), ap(8), dp(8) Context None