1Log::Report(3)        User Contributed Perl Documentation       Log::Report(3)
2
3
4

NAME

6       Log::Report - report a problem, with exceptions and translation support
7

INHERITANCE

9        Log::Report
10          is a Exporter
11

SYNOPSIS

13        # Invocation with 'mode' to get trace and verbose messages
14        use Log::Report mode => 'DEBUG';
15
16        # Usually invoked with a domain, which groups packages for translation
17        use Log::Report 'my-domain', %options;
18
19        # Interpolation syntax via String::Print
20        # First step to translations, once you need it.
21        print __x"my name is {name}", name => $n;  # print, so no exception
22        print __"Hello World\n";     # no interpolation, optional translation
23        print __x'Hello World';      # SYNTAX ERROR!!  ' is alternative for ::
24
25        # Functions replacing die/warn/carp, casting exceptions.
26        error "oops";                # exception like die(), no translation
27        -f $config or panic "Help!"; # alert/error/fault/info/...more
28
29        # Combined exception, interpolation, and optional translation
30        error __x"Help!";            # __x() creates ::Message object
31        error __x('gettext msgid', param => $value, ...)
32            if $condition;
33
34        # Also non fatal "exceptions" find their way to dispatchers
35        info __x"started {pid}", pid => $$;   # translatable
36        debug "$i was here!";        # you probably do not want to translate debug
37        panic "arrghhh";             # like Carp::Confess
38
39        # Many destinations for an exception message (may exist in parallel)
40        dispatcher PERL => 'default' # see Log::Report::Dispatcher: use die/warn
41          , reasons => 'NOTICE-';    # this dispatcher is already present at start
42
43        dispatcher SYSLOG => 'syslog'# also send to syslog
44          , charset => 'iso-8859-1'  # explicit character conversions
45          , locale => 'en_US';       # overrule user's locale
46
47        dispatcher close => 'default';  # stop default die/warn dispatcher
48
49        # Fill-in values, like Locale::TextDomain and gettext
50        # See Log::Report::Message section DETAILS
51        fault __x"cannot allocate {size} bytes", size => $size;
52        fault "cannot allocate $size bytes";     # no translation, ok
53        fault __x"cannot allocate $size bytes";  # not translatable, wrong
54
55        # Translation depending on count
56        # Leading and trailing whitespace stay magically outside translation
57        # tables.  @files in scalar context.  Special parameter with _
58        print __xn"found one file\n", "found {_count} files", @files;
59
60        # Borrow from an other text-domain (see Log::Report::Message)
61        print __x(+"errors in {line}", _domain => 'global', line => $line);
62
63        # catch errors (implements hidden eval/die)
64        try { error };
65        if($@) {...}      # $@ isa Log::Report::Dispatcher::Try
66        if(my $exception = $@->wasFatal)         # ::Exception object
67
68        # Language translations at the output component
69        # Translation management via Log::Report::Lexicon
70        use POSIX::1003::Locale qw/setlocale LC_ALL/;
71        setlocale(LC_ALL, 'nl_NL');
72        info __"Hello World!";      # in Dutch, if translation table found
73
74        # Exception classes, see Log::Report::Exception
75        try { error __x"something", _class => 'parsing,schema' };
76        if($@->wasFatal->inClass('parsing')) ...
77

DESCRIPTION

79       Get messages to users and logs.  "Log::Report" combines three tasks
80       which are closely related in one:
81
82       . logging (like Log::Log4Perl and syslog), and
83       . exceptions (like error and info), with
84       . translations (like "gettext" and Locale::TextDomain)
85
86       You do not need to use this module for all three reasons: pick what you
87       need now, maybe extend the usage later.  Read more about how and why in
88       the "DETAILS" section, below.  Especially, you should read about the
89       REASON parameter.
90
91       Also, you can study this module swiftly via the article published in
92       the German Perl "$foo-magazine".  English version:
93       http://perl.overmeer.net/log-report/papers/201306-PerlMagazine-article-en.html
94

FUNCTIONS

96   Report Production and Configuration
97       dispatcher( <$type, $name, %options>|<$command, @names> )
98           The "dispatcher" function controls access to dispatchers: the back-
99           ends which process messages, do the logging.  Dispatchers are
100           global entities, addressed by a symbolic $name.  Please read
101           Log::Report::Dispatcher as well.
102
103           The "Log::Report" suite has its own dispatcher @types, but also
104           connects to external dispatching frameworks.  Each need some
105           (minor) conversions, especially with respect to translation of
106           REASONS of the reports into log-levels as the back-end understands.
107
108           [1.10] When you open a dispatcher with a $name which is already in
109           use, that existing dispatcher gets closed.  Except when you have
110           given an 'dispatcher "do-not-reopen"' earlier, in which case the
111           first object stays alive, and the second attempt ignored. [1.11]
112           The automatically created default dispatcher will get replaced,
113           even when this option is given, by another dispatcher which is
114           named 'default'.
115
116           The %options are a mixture of parameters needed for the Log::Report
117           dispatcher wrapper and the settings of the back-end.  See
118           Log::Report::Dispatcher, the documentation for the back-end
119           specific wrappers, and the back-ends for more details.
120
121           Implemented COMMANDs are "close", "find", "list", "disable",
122           "enable", "mode", "filter", "needs", "active-try", and
123           "do-not-reopen".
124
125           Most commands are followed by a LIST of dispatcher @names to be
126           addressed.  For "mode" see section "Run modes"; it requires a MODE
127           argument before the LIST of NAMEs.  Non-existing names will be
128           ignored. When "ALL" is specified, then all existing dispatchers
129           will get addressed.  For "filter" see "Filters" in
130           Log::Report::Dispatcher; it requires a CODE reference before the
131           @names of the dispatchers which will have the it applied (defaults
132           to all).
133
134           With "needs", you only provide a REASON: it will return the list of
135           dispatchers which need to be called in case of a message with the
136           REASON is triggered.  The "active-try" [1.09] returns the closest
137           surrounding exception catcher, a Log::Report::Dispatcher::Try
138           object.
139
140           For both the creation as COMMANDs version of this method, all
141           objects involved are returned as LIST, non-existing ones skipped.
142           In SCALAR context with only one name, the one object is returned.
143
144           example: play with dispatchers
145
146            dispatcher Log::Dispatcher::File => mylog =>
147              , accept   => 'MISTAKE-'              # for wrapper
148              , locale   => 'pt_BR'                 # other language
149              , filename => 'logfile';              # for back-end
150
151            dispatcher close => 'mylog';            # cleanup
152            my $obj = dispatcher find => 'mylog';
153            my @obj = dispatcher 'list';
154            dispatcher disable => 'syslog';
155            dispatcher enable => 'mylog', 'syslog'; # more at a time
156            dispatcher mode => 'DEBUG', 'mylog';
157            dispatcher mode => 'DEBUG', 'ALL';
158            my $catcher = dispatcher 'active-try';
159            dispatcher 'do-not-reopen';
160
161            my @need_info = dispatcher needs => 'INFO';
162            if(dispatcher needs => 'INFO') ...      # anyone needs INFO
163
164            # Getopt::Long integration: see Log::Report::Dispatcher::mode()
165            dispatcher PERL => 'default', mode => 'DEBUG', accept => 'ALL'
166                if $debug;
167
168       report( [%options], $reason, $message|<STRING,$params>, )
169           The "report" function is sending (for some $reason) a $message to
170           be displayed or logged (by a `dispatcher').  This function is the
171           core for error(), info() etc functions, which are nicer names for
172           this exception throwing: better use those short names.
173
174           The $reason is a string like 'ERROR' (for function "error()").  The
175           $message is a Log::Report::Message object (which are created with
176           the special translation syntax like __x()).  The $message may also
177           be a plain string, or an Log::Report::Exception object. The
178           optional first parameter is a HASH which can be used to influence
179           the dispatchers.
180
181           The optional %options are listed below.  Quite differently from
182           other functions and methods, they have to be passed in a HASH as
183           first parameter.
184
185           This function returns the LIST of dispatchers which accepted the
186           $message.  When empty, no back-end has accepted it so the $message
187           was "lost".  Even when no back-end needs the message, the program
188           will still exit when there is a $reason to "die()".
189
190            -Option  --Default
191             errno     $! or 1
192             is_fatal  <depends on reason>
193             locale    undef
194             location  undef
195             stack     undef
196             to        undef
197
198           errno => INTEGER
199             When the $reason includes the error text (See "Run modes"), you
200             can overrule the error code kept in $!.  In other cases, the
201             return code defaults to 1 (historical UNIX behavior). When the
202             message $reason (combined with the run-mode) is severe enough to
203             stop the program, this value as return code of the program.  The
204             use of this option itself will not trigger an "die()".
205
206           is_fatal => BOOLEAN
207             Some logged exceptions are fatal, other aren't.  The default
208             usually is correct. However, you may want an error to be caught
209             (usually with try()), redispatch it to syslog, but without it
210             killing the main program.
211
212           locale => LOCALE
213             Use this specific locale, in stead of the user's preference.
214
215           location => STRING
216             When defined, this location is used in the display.  Otherwise,
217             it is determined automatically if needed.  An empty string will
218             disable any attempt to display this line.
219
220           stack => ARRAY
221             When defined, that data is used to display the call stack.
222             Otherwise, it is collected via "caller()" if needed.
223
224           to => NAME|ARRAY-of-NAMEs
225             Sent the $message only to the NAMEd dispatchers.  Ignore unknown
226             NAMEs.  Still, the dispatcher needs to be enabled and accept the
227             REASONs.
228
229           example: for use of report()
230
231            # long syntax example
232            report TRACE => "start processing now";
233            report INFO  => '500: ' . __'Internal Server Error';
234
235            # explicit dispatcher, no translation
236            report {to => 'syslog'}, NOTICE => "started process $$";
237            notice "started process $$", _to => 'syslog';   # same
238
239            # short syntax examples
240            trace "start processing now";
241            warning  __x'Disk {percent%.2f}% full', percent => $p
242                if $p > 97;
243
244            # error message, overruled to be printed in Brazilian
245            report {locale => 'pt_BR'}
246               , WARNING => "do this at home!";
247
248       try(CODE, %options)
249           Execute the CODE while blocking all dispatchers as long as it is
250           running.  The exceptions which occur while running the CODE are
251           caught until it has finished.  When there where no fatal errors,
252           the result of the CODE execution is returned.
253
254           After the CODE was tried, the $@ will contain a
255           Log::Report::Dispatcher::Try object, which contains the collected
256           messages.
257
258           Run-time errors from Perl and die's, croak's and confess's within
259           the program (which shouldn't appear, but you never know) are
260           collected into an Log::Report::Message object, using
261           Log::Report::Die.
262
263           The %options are passed to the constructor of the try-dispatcher,
264           see Log::Report::Dispatcher::Try::new().  For instance, you may
265           like to add "mode => 'DEBUG'", or "accept => 'ERROR-'".
266
267           Be warned that the parameter to "try" is a CODE reference.  This
268           means that you shall not use a comma after the block when there are
269           %options specified.  On the other hand, you shall use a semi-colon
270           after the block if there are no arguments.
271
272           Be warned that the {} are interpreted as subroutine, which means
273           that, for instance, it has its own @_.  The manual-page of
274           Try::Tiny lists a few more side-effects of this.
275
276           example:
277
278            my $x = try { 3/$x };  # mind the ';' !!
279            if($@) {               # signals something went wrong
280
281            if(try {...}) {        # block ended normally, returns bool
282
283            try { ... }            # no comma!!
284               mode => 'DEBUG', accept => 'ERROR-';
285
286            try sub { ... },       # with comma, also \&function
287               mode => 'DEBUG', accept => 'ALL';
288
289            my $response = try { $ua->request($request) };
290            if(my $e = $@->wasFatal) ...
291
292   Abbreviations for report()
293       The following functions are all wrappers for calls to report(), and
294       available when "syntax is SHORT" (by default, see import()).  You
295       cannot specify additional options to influence the behavior of
296       "report()", which are usually not needed anyway.
297
298       alert($message)
299           Short for "report ALERT => $message"
300
301       assert($message)
302           Short for "report ASSERT => $message"
303
304       error($message)
305           Short for "report ERROR => $message"
306
307       failure($message)
308           Short for "report FAILURE => $message"
309
310       fault($message)
311           Short for "report FAULT => $message"
312
313       info($message)
314           Short for "report INFO => $message"
315
316       mistake($message)
317           Short for "report MISTAKE => $message"
318
319       notice($message)
320           Short for "report NOTICE => $message"
321
322       panic($message)
323           Short for "report PANIC => $message"
324
325       trace($message)
326           Short for "report TRACE => $message"
327
328       warning($message)
329           Short for "report WARNING => $message"
330
331   Messages (optionally translatable)
332       Even when you do not support translations (yet) you may want to use
333       message objects to improve the logging feature. For instance, you get
334       very powerful interpolation from String::Print.
335
336       The language translations are initiate by limited set of functions
337       which contain two under-scores ("__") in their name.  Most of them
338       return a Log::Report::Message object.
339
340       Be warned(1) that -in general- its considered very bad practice to
341       combine multiple translations into one message: translating may also
342       affect the order of the translated components. Besides, when the person
343       which translates only sees smaller parts of the text, his (or her) job
344       becomes more complex.  So:
345
346        print __"Hello" . ', ' . __"World!";  # works, but to be avoided
347        print __"Hello, World!";              # preferred, complete sentence
348
349       The the former case, tricks with overloading used by the
350       Log::Report::Message objects will still make delayed translations work.
351
352       In normal situations, it is not a problem to translate interpolated
353       values:
354
355        print __"the color is {c}", c => __"red";
356
357       Be warned(2) that using "__'Hello'" will produce a syntax error like
358       "String found where operator expected at .... Can't find string
359       terminator "'" anywhere before EOF".  The first quote is the cause of
360       the complaint, but the second generates the error.  In the early days
361       of Perl, the single quote was used to separate package name from
362       function name, a role which was later replaced by a double-colon.  So
363       "__'Hello'" gets interpreted as "__::Hello '".  Then, there is a
364       trailing single quote which has no counterpart.
365
366       N__($msgid)
367           Label to indicate that the string is a text which will be
368           translated later.  The function itself does nothing.  See also
369           N__w().
370
371           This no-op function is used as label to the xgettext program to
372           build the translation tables.
373
374           example: how to use N__()
375
376            # add three msgids to the translation table
377            my @colors = (N__"red", N__"green", N__"blue");
378            my @colors = N__w "red green blue";   # same
379            print __ $colors[1];                  # translate green
380
381            # using __(), would work as well
382            my @colors = (__"red", __"green", __"blue");
383            print $colors[1];
384            # however: this will always create all Log::Report::Message objects,
385            # where maybe only one is used.
386
387       N__n($single_msgid, $plural_msgid)
388           Label to indicate that the two MSGIDs are related, the first as
389           single, the seconds as its plural.  Only used to find the text
390           fragments to be translated.  The function itself does nothing.
391
392           example: how to use N__n()
393
394            my @save = N__n "save file", "save files";
395            my @save = (N__n "save file", "save files");
396            my @save = N__n("save file", "save files");
397
398            # be warned about SCALARs in prototype!
399            print __n @save, $nr_files;  # wrong!
400            print __n $save[0], $save[1], @files, %vars;
401
402       N__w(STRING)
403           This extension to the Locale::TextDomain syntax, is a combined "qw"
404           (list of quoted words) and N__() into a list of translatable words.
405
406           example: of N__w()
407
408             my @colors = (N__"red", N__"green", N__"blue");
409             my @colors = N__w"red green blue";  # same
410             print __ $colors[1];
411
412       __($msgid)
413           This function (name is two under-score characters) will cause the
414           $msgid to be replaced by the translations when doing the actual
415           output.  Returned is a Log::Report::Message object, which will be
416           used in translation later.  Translating is invoked when the object
417           gets stringified.  When you have no translation tables, the $msgid
418           will be shown untranslated.
419
420           If you need options for Log::Report::Message::new() then use __x();
421           the prototype of this function does not permit parameters: it is a
422           prefix operator!
423
424           example: how to use __()
425
426            print __"Hello World";      # translated into user's language
427            print __'Hello World';      # syntax error!
428            print __('Hello World');    # ok, translated
429            print __"Hello", " World";  # World not translated
430
431            my $s = __"Hello World";    # creates object, not yet translated
432            print ref $s;               # Log::Report::Message
433            print $s;                   # ok, translated
434            print $s->toString('fr');   # ok, forced into French
435
436       __n($msgid, $plural_msgid, $count, PAIRS)
437           It depends on the value of $count (and the selected language) which
438           text will be displayed.  When translations can not be performed,
439           then $msgid will be used when $count is 1, and PLURAL_MSGSID in
440           other cases.  However, some languages have more complex schemes
441           than English.
442
443           The PAIRS are options for Log::Report::Message::new() and variables
444           to be filled in.
445
446           example: how to use __n()
447
448            print __n "one", "more", $a;
449            print __n("one", "more", $a), "\n";
450            print +(__n "one", "more", $a), "\n";
451
452            # new-lines are ignore at lookup, but printed.
453            print __n "one\n", "more\n", $a;
454
455            # count is in scalar context
456            # the value is also available as _count
457            print __n "found one\n", "found {_count}\n", @r;
458
459            # ARRAYs and HASHes are counted
460            print __n "one", "more", \@r;
461
462       __nx($msgid, $plural_msgid, $count, PAIRS)
463           It depends on the value of $count (and the selected language) which
464           text will be displayed.  See details in __n().  After translation,
465           the VARIABLES will be filled-in.
466
467           The PAIRS are options for Log::Report::Message::new() and variables
468           to be filled in.
469
470           example: how to use __nx()
471
472            print __nx "one file", "{_count} files", $nr_files;
473            print __nx "one file", "{_count} files", @files;
474
475            local $" = ', ';
476            print __nx "one file: {f}", "{_count} files: {f}", @files, f => \@files;
477
478       __x($msgid, PAIRS)
479           Translate the $msgid and then interpolate the VARIABLES in that
480           string.  Of course, translation and interpolation is delayed as
481           long as possible.  Both OPTIONS and VARIABLES are key-value pairs.
482
483           The PAIRS are options for Log::Report::Message::new() and variables
484           to be filled in.
485
486       __xn($single_msgid, $plural_msgid, $count, $paurs)
487           Same as __nx(), because we have no preferred order for 'x' and 'n'.
488
489       Messages with msgctxt
490
491       In Log::Report, the message context (mgsctxt in the PO-files --in the
492       translation tables) can be used in a very powerful way.  Read all about
493       it in Log::Report::Translator::Context
494
495       The msgctxt versions of the tranditional gettext infrastructure are far
496       less useful for Log::Report, because we can easily work with different
497       text domains within the same program.  That should avoid most of the
498       accidental translation conflicts between components of the code.
499
500       Just for compatibility with Locale::TextDomain and completeness, the
501       'p' versions of above methods are supported.  See examples for these
502       functions in Locale::TextDomain.
503
504       Warnings: Functions "N__p()" and "N__np()" seem not to be usable in
505       reality, hence not implemented.  The script xgettext-perl and
506       Log::Report::Extract::PerlPPI (both in the Log::Report::Lexicon
507       distribution) do not yet support these functions.
508
509       __np($msgctxt, $msgid, $plural, count)
510       __npx($msgctxt, $msgid, $plural, count, PAIRS)
511       __p($msgctxt, $msgid)
512       __px($msgctxt, $msgid, PAIRS)
513
514   Configuration
515       $obj->import( [$level,][$domain,] %options )
516           The import is automatically called when the package is compiled.
517           For all packages but one in your distribution, it will only contain
518           the name of the $domain.
519
520           For one package, the import list may additionally contain
521           textdomain configuration %options.  These %options are used for all
522           packages which use the same $domain.  These are alternatives:
523
524             # Do not use variables in the %*config!  They are not yet initialized
525             # when Log::Report->import is run!!!
526             use Log::Report 'my-domain', %config, %domain_config;
527
528             use Log::Report 'my-domain', %config;
529             textdomain 'my-domain', %domain_config;   # vars allowed
530
531           The latter syntax has major advantages, when the configuration of
532           the domain is determined at run-time.  It is probably also easier
533           to understand.
534
535           See Log::Report::Domain::configure(), for the list of %options for
536           the domain configuration.  Here, we only list the options which are
537           related to the normal import behavior.
538
539           The export $level is a plus (+) followed by a number, for instance
540           +1, to indicate to on which caller level we need to work.  This is
541           used in Log::Report::Optional.  It defaults to '0': my direct
542           caller.
543
544            -Option       --Default
545             import         undef
546             message_class  Log::Report::Message
547             mode           'NORMAL'
548             syntax         'SHORT'
549
550           import => FUNCTION|ARRAY
551             [0.998] When not specified, the "syntax" option determines the
552             list of functions which are being exported.  With this option,
553             the "syntax" option is ignored and only the specified FUNCTION(s)
554             are imported.
555
556           message_class => CLASS
557             [1.08] Use a more powerful message object class, for instance
558             because your messages need extra attributes.  The provided CLASS
559             must extend Log::Report::Message
560
561           mode => LEVEL
562             This sets the default mode for all created dispatchers.  You can
563             also selectively change the output mode, like
564              dispatcher PERL => 'default', mode => 3
565
566           syntax => 'REPORT'|'SHORT'|'LONG'
567             The SHORT syntax will add the report abbreviations (like function
568             error()) to your name-space.  Otherwise, each message must be
569             produced with report(). "LONG" is an alternative to "REPORT":
570             both do not pollute your namespace with the useful abbrev
571             functions.
572
573           example: of import
574
575            use Log::Report mode => 3;     # '3' or 'DEBUG'
576
577            use Log::Report 'my-domain';   # in each package producing messages
578
579            use Log::Report 'my-domain'    # in one package, top of distr
580             , mode            => 'VERBOSE'
581             , syntax          => 'REPORT' # report ERROR, not error()
582             , translator      => Log::Report::Translator::POT->new
583                ( lexicon => '/home/mine/locale'  # translation tables
584                )
585             , native_language => 'nl_NL'; # untranslated msgs are Dutch
586
587            use Log::Report import => 'try';      # or ARRAY of functions
588
589       textdomain( <[$name],$config>|<$name, 'DELETE'|'EXISTS'>|$domain )
590           [1.00] Without CONFIGuration, this returns the Log::Report::Domain
591           object which administers the $domain, by default the domain
592           effective in the scope of the package.
593
594           A very special case is "DELETE", which will remove the domain
595           configuration. [1.20] "EXISTS" will check for existence: when it
596           exists, it will be returned, but a domain will not be automagically
597           created.
598
599           [1.20] You may also pass a pre-configured domain.
600
601   Reasons
602       Log::Report->needs( $reason, [$reasons] )
603           Returns true when the reporter needs any of the $reasons, when any
604           of the active dispatchers is collecting messages in the specified
605           level.  This is useful when the processing of data for the message
606           is relatively expensive, but for instance only required in debug
607           mode.
608
609           example:
610
611             if(Log::Report->needs('TRACE'))
612             {   my @args = ...expensive calculation...;
613                 trace "your options are: @args";
614             }
615

DETAILS

617   Introduction
618       Getting messages to users and logs. The distincting concept of this
619       module, is that three tasks which are strongly related are merged into
620       one simple syntax.  The three tasks:
621
622       produce some text on a certain condition,
623       translate it to the proper language, and
624       deliver it in some way to a user.
625
626       Text messages in Perl are produced by commands like "print", "die",
627       "warn", "carp", or "croak".  But where is that output directed to?
628       Translations is hard.  There is no clean exception mechanism.
629
630       Besides, the "print"/"warn"/"die" together produce only three different
631       output "levels" with a message.  Think of the variation syslog offers:
632       more than 7 levels.  Many people manually implement their own tricks to
633       get additional levels, like verbose and debug flags.  Log::Report
634       offers that variety.
635
636       The (optional) translations use the beautiful syntax defined by
637       Locale::TextDomain, with some own extensions (of course).  A very
638       important difference is that translations are delayed till the delivery
639       step: until a dispatcher actually writes your message into a file,
640       sends it to syslog, or shows it on the screen.  This means that the
641       pop-up in the graphical interface of the user may show the text in the
642       language of the user --say Chinese in utf8--, but at the same time
643       syslog may write the latin1 English version of the same message.
644
645   Background ideas
646       The following ideas are the base of this implementation:
647
648       . simplification
649           Handling errors and warnings is probably the most labor-intensive
650           task for a programmer: when programs are written correctly, up-to
651           three-quarters of the code is related to testing, reporting, and
652           handling (problem) conditions.  Simplifying the way to create
653           reports, simplifies programming and maintenance.
654
655       . multiple dispatchers
656           It is not the location where the (for instance) error occurs which
657           determines what will happen with the text, but the main application
658           which uses the the complaining module has control.  Messages have a
659           reason.  Based on the `reason' classification, they can get
660           ignored, send to one or multiple dispatchers, like Log::Dispatch,
661           Log::Log4perl, or UNIX syslog.
662
663       . delayed translations
664           The background ideas are that of Locale::TextDomain, based on
665           "gettext()".  However, in the "Log::Report" infrastructure,
666           translations are postponed until the text is dispatched to a screen
667           or log-file; the same report can be sent to syslog in (for
668           instance) English and to the user interface in Dutch.
669
670       . context sensitive
671           Using contexts, you can set-up how to translate or rewrite
672           messages, to improve messages.  A typical problem is whether to use
673           gender in text (use 'his' or 'her'): you can set a gender in a
674           context, and the use translation tables to pick the right one.
675
676   Error handling models
677       There are two approaches to handling errors and warnings.  In the first
678       approach, as produced by "die", "warn" and the "carp" family of
679       commands, the program handles the problem immediately on the location
680       where the problem appears.  In the second approach, an exception is
681       thrown on the spot where the problem is created, and then somewhere
682       else in the program the condition is handled.
683
684       The implementation of exceptions in Perl5 is done with a eval-die pair:
685       on the spot where the problem occurs, "die" is called.  But, because of
686       the execution of that routine is placed within an "eval", the program
687       as a whole will not die, just the execution of a part of the program
688       will seize.  However, what if the condition which caused the routine to
689       die is solvable on a higher level?  Or what if the user of the code
690       doesn't bother that a part fails, because it has implemented
691       alternatives for that situation?  Exception handling is quite clumsy in
692       Perl5.
693
694       The "Log::Report" set of distributions let modules concentrate on the
695       program flow, and let the main program decide on the report handling
696       model.  The infrastructure to translate messages into multiple
697       languages, whether to create exceptions or carp/die, to collect longer
698       explanations with the messages, to log to mail or syslog, and so on, is
699       decided in pluggable back-ends.
700
701       The Reason for the report
702
703       Traditionally, perl has a very simple view on error reports: you either
704       have a warning or an error.  However, it would be much clearer for
705       user's and module-using applications, when a distinction is made
706       between various causes.  For instance, a configuration error is quite
707       different from a disk-full situation.  In "Log::Report", the produced
708       reports in the code tell what is wrong.  The main application defines
709       loggers, which interpret the cause into (syslog) levels.
710
711       Defined by "Log::Report" are
712
713       . trace (debug, program)
714           The message will be used when some logger has debugging enabled.
715           The messages show steps taken by the program, which are of interest
716           by the developers and maintainers of the code, but not for end-
717           users.
718
719       . assert (program)
720           Shows an unexpected condition, but continues to run.  When you want
721           the program to abort in such situation, that use "panic".
722
723       . info (verbose, program)
724           These messages show larger steps in the execution of the program.
725           Experienced users of the program usually do not want to see all
726           these intermediate steps.  Most programs will display info messages
727           (and higher) when some "verbose" flag is given on the command-line.
728
729       . notice (program)
730           An user may need to be aware of the program's accidental smart
731           behavior, for instance, that it initializes a lasting "Desktop"
732           directory in your home directory.  Notices should be sparse.
733
734       . warning (program)
735           The program encountered some problems, but was able to work around
736           it by smart behavior.  For instance, the program does not
737           understand a line from a log-file, but simply skips the line.
738
739       . mistake (user)
740           When a user does something wrong, but what is correctable by smart
741           behavior of the program.  For instance, in some configuration file,
742           you can fill-in "yes" or "no", but the user wrote "yeah".  The
743           program interprets this as "yes", producing a mistake message as
744           warning.
745
746           It is much nicer to tell someone that he/she made a mistake, than
747           to call that an error.
748
749       . error (user)
750           The user did something wrong, which is not automatically
751           correctable or the program is not willing to correct it
752           automatically for reasons of code quality.  For instance, an
753           unknown option flag is given on the command-line.  These are
754           configuration issues, and have no useful value in $!.  The program
755           will be stopped, usually before taken off.
756
757       . fault (system)
758           The program encountered a situation where it has no work-around.
759           For instance, a file cannot be opened to be written.  The cause of
760           that problem can be some user error (i.e. wrong filename), or
761           external (you accidentally removed a directory yesterday).  In any
762           case, the $! ($ERRNO) variable is set here.
763
764       . alert (system)
765           Some external cause disturbs the execution of the program, but the
766           program stays alive and will try to continue operation.  For
767           instance, the connection to the database is lost.  After a few
768           attempts, the database can be reached and the program continues as
769           if nothing happened.  The cause is external, so $! is set.
770           Usually, a system administrator needs to be informed about the
771           problem.
772
773       . failure (system)
774           Some external cause makes it impossible for this program to
775           continue.  $! is set, and usually the system administrator wants to
776           be informed.  The program will die.
777
778           The difference with "fault" is subtile and not always clear.  A
779           fault reports an error returned by an operating system call, where
780           the failure would report an operational problem, like a failing
781           mount.
782
783       . panic (program)
784           All above report classes are expected: some predictable situation
785           is encountered, and therefore a message is produced.  However,
786           programs often do some internal checking.  Of course, these
787           conditions should never be triggered, but if they do... then we can
788           only stop.
789
790           For instance, in an OO perl module, the base class requires all
791           sub-classes to implement a certain method.  The base class will
792           produce a stub method with triggers a panic when called.  The non-
793           dieing version of this test "assert".
794
795       Debugging or being "verbose" are run-time behaviors, and have nothing
796       directly to do with the type of message which is produced.  These two
797       are modes which can be set on the dispatchers: one dispatcher may be
798       more verbose that some other.
799
800       On purpose, we do not use the terms "die" or "fatal", because the
801       dispatcher can be configured what to do in cause of which condition.
802       For instance, it may decide to stop execution on warnings as well.
803
804       The terms "carp" and "croak" are avoided, because the program cause
805       versus user cause distinction (warn vs carp) is reflected in the use of
806       different reasons.  There is no need for "confess" and "croak" either,
807       because the dispatcher can be configured to produce stack-trace
808       information (for a limited sub-set of dispatchers)
809
810       Report levels
811
812       Various frameworks used with perl programs define different labels to
813       indicate the reason for the message to be produced.
814
815        Perl5 Log::Dispatch Syslog Log4Perl Log::Report
816        print   0,debug     debug  debug    trace
817        print   0,debug     debug  debug    assert
818        print   1,info      info   info     info
819        warn\n  2,notice    notice info     notice
820        warn    3,warning   warn   warn     mistake
821        carp    3,warning   warn   warn     warning
822        die\n   4,error     err    error    error
823        die     5,critical  crit   fatal    fault
824        croak   6,alert     alert  fatal    alert
825        croak   7,emergency emerg  fatal    failure
826        confess 7,emergency emerg  fatal    panic
827
828       Run modes
829
830       The run-mode change which messages are passed to a dispatcher, but from
831       a different angle than the dispatch filters; the mode changes
832       behavioral aspects of the messages, which are described in detail in
833       "Processing the message" in Log::Report::Dispatcher.  However, it
834       should behave as you expect: the DEBUG mode shows more than the VERBOSE
835       mode, and both show more than the NORMAL mode.
836
837       . Example: extract run mode from Getopt::Long
838
839       The "GetOptions()" function will count the number of "v" options on the
840       command-line when a "+" is after the option name.
841
842        use Log::Report;
843        use Getopt::Long qw(:config no_ignore_case bundling);
844
845        my $mode;    # defaults to NORMAL
846        GetOptions 'v+'        => \$mode
847                 , 'verbose=i' => \$mode
848                 , 'mode=s'    => \$mode
849            or exit 1;
850
851        dispatcher 'PERL', 'default', mode => $mode;
852
853       Now, "-vv" will set $mode to 2, as will "--verbose 2" and "--verbose=2"
854       and "--mode=ASSERT".  Of course, you do not need to provide all these
855       options to the user: make a choice.
856
857       . Example: the mode of a dispatcher
858
859        my $mode = dispatcher(find => 'myname')->mode;
860
861       . Example: run-time change mode of a dispatcher
862
863       To change the running mode of the dispatcher, you can do
864         dispatcher mode => DEBUG => 'myname';
865
866       However, be warned that this does not change the types of messages
867       accepted by the dispatcher!  So: probably you will not receive the
868       trace, assert, and info messages after all.  So, probably you need to
869       replace the dispatcher with a new one with the same name:
870         dispatcher FILE => 'myname', to => ..., mode => 'DEBUG';
871
872       This may reopen connections (depends on the actual dispatcher), which
873       might be not what you wish to happened.  In that case, you must take
874       the following approach:
875
876         # at the start of your program
877         dispatcher FILE => 'myname', to => ...
878            , accept => 'ALL';    # overrule the default 'NOTICE-' !!
879
880         # now it works
881         dispatcher mode => DEBUG => 'myname';    # debugging on
882         ...
883         dispatcher mode => NORMAL => 'myname';   # debugging off
884
885       Of course, this comes with a small overall performance penalty.
886
887       Exceptions
888
889       The simple view on live says: you 're dead when you die.  However, more
890       complex situations try to revive the dead.  Typically, the "die" is
891       considered a terminating exception, but not terminating the whole
892       program, but only some logical block.  Of course, a wrapper round that
893       block must decide what to do with these emerging problems.
894
895       Java-like languages do not "die" but throw exceptions which contain the
896       information about what went wrong.  Perl modules like
897       "Exception::Class" simulate this.  It's a hassle to create exception
898       class objects for each emerging problem, and the same amount of work to
899       walk through all the options.
900
901       Log::Report follows a simpler scheme.  Fatal messages will "die", which
902       is caught with "eval", just the Perl way (used invisible to you).
903       However, the wrapper gets its hands on the message as the user has
904       specified it: untranslated, with all unprocessed parameters still at
905       hand.
906
907        try { fault __x "cannot open file {file}", file => $fn };
908        if($@)                         # is Log::Report::Dispatcher::Try
909        {   my $cause = $@->wasFatal;  # is Log::Report::Exception
910            $cause->throw if $cause->message->msgid =~ m/ open /;
911            # all other problems ignored
912        }
913
914       See Log::Report::Dispatcher::Try and Log::Report::Exception.
915
916   Comparison
917       Some notes on differences between the Log::Report approach and other
918       Perl concepts.
919
920       die/warn/Carp
921
922       Perl's built-in exception system is very primitive: "die" and "warn".
923       Most programming languages provide a much more detailed exception
924       mechanism.
925
926       A typical perl program can look like this:
927
928        my $dir = '/etc';
929
930        File::Spec->file_name is_absolute($dir)
931            or die "ERROR: directory name must be absolute.\n";
932
933        -d $dir
934            or die "ERROR: what platform are you on?";
935
936        until(opendir DIR, $dir)
937        {   warn "ERROR: cannot read system directory $dir: $!";
938            sleep 60;
939        }
940
941        print "Processing directory $dir\n"
942            if $verbose;
943
944        while(defined(my $file = readdir DIR))
945        {   if($file =~ m/\.bak$/)
946            {   warn "WARNING: found backup file $dir/$f\n";
947                next;
948            }
949
950            die "ERROR: file $dir/$file is binary"
951                if $debug && -B "$dir/$file";
952
953            print "DEBUG: processing file $dir/$file\n"
954                if $debug;
955
956            open FILE, "<", "$dir/$file"
957                or die "ERROR: cannot read from $dir/$f: $!";
958
959            close FILE
960                or croak "ERROR: read errors in $dir/$file: $!";
961        }
962
963       Where "die", "warn", and "print" are used for various tasks.  With
964       "Log::Report", you would write
965
966        use Log::Report;
967
968        # can be left-out when there is no debug/verbose
969        dispatcher PERL => 'default', mode => 'DEBUG';
970
971        my $dir = '/etc';
972
973        File::Spec->file_name is_absolute($dir)
974            or mistake "directory name must be absolute";
975
976        -d $dir
977            or panic "what platform are you on?";
978
979        until(opendir DIR, $dir)
980        {   alert "cannot read system directory $dir";
981            sleep 60;
982        }
983
984        info "Processing directory $dir";
985
986        while(defined(my $file = readdir DIR))
987        {   if($file =~ m/\.bak$/)
988            {   notice "found backup file $dir/$f";
989                next;
990            }
991
992            assert "file $dir/$file is binary"
993                if -B "$dir/$file";
994
995            trace "processing file $dir/$file";
996
997            unless(open FILE, "<", "$dir/$file")
998            {   error "no permission to read from $dir/$f"
999                    if $!==ENOPERM;
1000                fault "unable to read from $dir/$f";
1001            }
1002
1003            close FILE
1004                or failure "read errors in $dir/$file";
1005        }
1006
1007       A lot of things are quite visibly different, and there are a few
1008       smaller changes.  There is no need for a new-line after the text of the
1009       message.  When applicable (error about system problem), then the $! is
1010       added automatically.
1011
1012       Log::Dispatch and Log::Log4perl
1013
1014       The two major logging frameworks for Perl are Log::Dispatch and
1015       Log::Log4perl; both provide a pluggable logging interface.
1016
1017       Both frameworks do not have (gettext or maketext) language translation
1018       support, which has various consequences.  When you wish for to report
1019       in some other language, it must be translated before the logging
1020       function is called.   This may mean that an error message is produced
1021       in Chinese, and therefore also ends-up in the syslog file in Chinese.
1022       When this is not your language, you have a problem.
1023
1024       Log::Report translates only in the back-end, which means that the user
1025       may get the message in Chinese, but you get your report in your beloved
1026       Dutch.  When no dispatcher needs to report the message, then no time is
1027       lost in translating.
1028
1029       With both logging frameworks, you use terminology comparable to syslog:
1030       the module programmer determines the seriousness of the error message,
1031       not the application which integrates multiple modules.  This is the way
1032       perl programs usually work, but often the cause for inconsequent user
1033       interaction.
1034
1035       Locale::gettext and Locate::TextDomain
1036
1037       Both on GNU gettext based implementations can be used as translation
1038       frameworks.  Locale::TextDomain syntax is supported, with quite some
1039       extensions. Read the excellent documentation of Locale::Textdomain.
1040       Only the tried access via "$__" and "%__" are not supported.
1041
1042       The main difference with these modules is the moment when the
1043       translation takes place.  In Locale::TextDomain, an "__x()" will result
1044       in an immediate translation request via "gettext()".  "Log::Report"'s
1045       version of "__x()" will only capture what needs to be translated in an
1046       object.  When the object is used in a print statement, only then the
1047       translation will take place.  This is needed to offer ways to send
1048       different translations of the message to different destinations.
1049
1050       To be able to postpone translation, objects are returned which
1051       stringify into the translated text.
1052

DIAGNOSTICS

1054       Error: in SCALAR context, only one dispatcher name accepted
1055           The dispatcher() method returns the Log::Report::Dispatcher objects
1056           which it has accessed.  When multiple names where given, it wishes
1057           to return a LIST of objects, not the count of them.
1058

SEE ALSO

1060       This module is part of Log-Report distribution version 1.29, built on
1061       November 08, 2019. Website: http://perl.overmeer.net/CPAN/
1062

LICENSE

1064       Copyrights 2007-2019 by [Mark Overmeer <markov@cpan.org>]. For other
1065       contributors see ChangeLog.
1066
1067       This program is free software; you can redistribute it and/or modify it
1068       under the same terms as Perl itself.  See http://dev.perl.org/licenses/
1069
1070
1071
1072perl v5.30.1                      2019-11-08                    Log::Report(3)
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