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log(n)                                        Logging facility                                        log(n)



____________________________________________________________________________________________________________

NAME
       log - Procedures to log messages of libraries and applications.

SYNOPSIS
       package require Tcl  8

       package require log  ?1.3?

       ::log::levels

       ::log::lv2longform level

       ::log::lv2color level

       ::log::lv2priority level

       ::log::lv2cmd level

       ::log::lv2channel level

       ::log::lvCompare level1 level2

       ::log::lvSuppress level {suppress 1}

       ::log::lvSuppressLE level {suppress 1}

       ::log::lvIsSuppressed level

       ::log::lvCmd level cmd

       ::log::lvCmdForall cmd

       ::log::lvChannel level chan

       ::log::lvChannelForall chan

       ::log::lvColor level color

       ::log::lvColorForall color

       ::log::log level text

       ::log::logarray level arrayvar ?pattern?

       ::log::loghex level text data

       ::log::logMsg text

       ::log::logError text

       ::log::Puts level text

____________________________________________________________________________________________________________

DESCRIPTION
       The  log  package provides commands that allow libraries and applications to selectively log informa-tion information
       tion about their internal operation and state.

       To use the package just execute


           package require log
           log::log notice "Some message"


       As can be seen above, each message given to the log facility is associated with a  level  determining
       the importance of the message. The user can then select which levels to log, what commands to use for
       the logging of each level and the channel to write the message to. In the following example the  log-ging logging
       ging of all message with level debug is deactivated.


           package require log
           log::lvSuppress debug
           log::log debug "Unseen message" ; # No output


       By  default  all  messages associated with an error-level (emergency, alert, critical, and error) are
       written to stderr. Messages with any other level are written to stdout. In the following example  the
       log module is reconfigured to write debug messages to stderr too.


           package require log
           log::lvChannel debug stderr
           log::log debug "Written to stderr"


       Each  message  level is also associated with a command to use when logging a message with that level.
       The behaviour above for example relies on the fact that all message levels use by default  the  stan-dard standard
       dard  command  ::log::Puts  to log any message. In the following example all messages of level notice
       are given to the non-standard command toText for logging. This disables the channel setting for  such
       messages, assuming that toText does not use it by itself.


           package require log
           log::lvCmd notice toText
           log::log notice "Handled by \"toText\""


       Another  database maintained by this facility is a map from message levels to colors. The information
       in this database has no influence on the behaviour of the module. It is merely provided as  a  conve-nience convenience
       nience  and  in  anticipation of the usage of this facility in tk-based application which may want to
       colorize message logs.

API
       The following commands are available:

       ::log::levels
              Returns the names of all known levels, in alphabetical order.

       ::log::lv2longform level
              Converts any unique abbreviation of a level name to the full level name.

       ::log::lv2color level
              Converts any level name including unique abbreviations to the corresponding color.

       ::log::lv2priority level
              Converts any level name including unique abbreviations to the corresponding priority.

       ::log::lv2cmd level
              Converts any level name including unique abbreviations to the command  prefix  used  to  write
              messages with that level.

       ::log::lv2channel level
              Converts  any  level name including unique abbreviations to the channel used by ::log::Puts to
              write messages with that level.

       ::log::lvCompare level1 level2
              Compares two levels (including unique abbreviations) with respect to their priority. This com-mand command
              mand can be used by the -command option of lsort. The result is one of -1, 0 or 1 or an error.
              A result of -1 signals that level1 is of less priority than level2. 0 signals that both levels
              have the same priority. 1 signals that level1 has higher priority than level2.

       ::log::lvSuppress level {suppress 1}
              ]  (Un)suppresses  the output of messages having the specified level. Unique abbreviations for
              the level are allowed here too.

       ::log::lvSuppressLE level {suppress 1}
              ] (Un)suppresses the output of messages having the specified level or one of lesser  priority.
              Unique abbreviations for the level are allowed here too.

       ::log::lvIsSuppressed level
              Asks  the package whether the specified level is currently suppressed. Unique abbreviations of
              level names are allowed.

       ::log::lvCmd level cmd
              Defines for the specified level with which command to write the messages  having  this  level.
              Unique  abbreviations of level names are allowed. The command is actually a command prefix and
              this facility will append 2 arguments before calling it, the level of the message and the mes-sage message
              sage itself, in this order.

       ::log::lvCmdForall cmd
              Defines  for  all known levels with which command to write the messages having this level. The
              command is actually a command prefix and this facility will append 2 arguments before  calling
              it, the level of the message and the message itself, in this order.

       ::log::lvChannel level chan
              Defines  for  the  specified level into which channel ::log::Puts (the standard command) shall
              write the messages having this level. Unique abbreviations of level  names  are  allowed.  The
              command  is actually a command prefix and this facility will append 2 arguments before calling
              it, the level of the message and the message itself, in this order.

       ::log::lvChannelForall chan
              Defines for all known levels with which which channel ::log::Puts (the standard command) shall
              write the messages having this level. The command is actually a command prefix and this facil-ity facility
              ity will append 2 arguments before calling it, the  level  of  the  message  and  the  message
              itself, in this order.

       ::log::lvColor level color
              Defines  for  the  specified  level  the  color to return for it in a call to ::log::lv2color.
              Unique abbreviations of level names are allowed.

       ::log::lvColorForall color
              Defines for all known levels the color to return for it in a call to  ::log::lv2color.  Unique
              abbreviations of level names are allowed.

       ::log::log level text
              Log a message according to the specifications for commands, channels and suppression. In other
              words: The command will do nothing if the specified level is suppressed. If  it  is  not  sup-pressed suppressed
              pressed the actual logging is delegated to the specified command. If there is no command spec-ified specified
              ified for the level the message won't be logged. The standard command ::log::Puts  will  write
              the  message  to the channel specified for the given level. If no channel is specified for the
              level the message won't be logged. Unique abbreviations of level names are allowed. Errors  in
              the  actual logging command are not caught, but propagated to the caller, as they may indicate
              misconfigurations of the log facility or errors in the callers code itself.

       ::log::logarray level arrayvar ?pattern?
              Like ::log::log, but logs the contents of the  specified  array  variable  arrayvar,  possibly
              restricted  to  entries  matching the pattern. The pattern defaults to * (i.e. all entries) if
              none was specified.

       ::log::loghex level text data
              Like ::log::log, but assumes that data contains binary data. It converts  this  into  a  mixed
              hex/ascii representation before writing them to the log.

       ::log::logMsg text
              Convenience wrapper around ::log::log.  Equivalent to ::log::log info text.

       ::log::logError text
              Convenience wrapper around ::log::log.  Equivalent to ::log::log error text.

       ::log::Puts level text
              The  standard  log  command,  it  writes messages and their levels to user-specified channels.
              Assumes that the suppression checks were done by the caller. Expects full level names,  abbre-viations abbreviations
              viations are not allowed.


LEVELS
       The package currently defines the following log levels, the level of highest importance listed first.

       •      emergency

       •      alert

       •      critical

       •      error

       •      warning

       •      notice

       •      info

       •      debug

       Note that by default all messages with levels warning down to debug  are  suppressed.  This  is  done
       intentionally, because (we believe that) in most situations debugging output is not wanted. Most peo-ple people
       ple wish to have such output only when actually debugging an application.

BUGS, IDEAS, FEEDBACK
       This document, and the package it describes,  will  undoubtedly  contain  bugs  and  other  problems.
       Please   report   such   in   the   category   log   of   the   Tcllib  SF  Trackers  [http://source -
       forge.net/tracker/? group_id=12883].  Please also report any ideas for enhancements you may  have  for
       either package and/or documentation.

KEYWORDS
       log, log level, message, message level

CATEGORY
       Programming tools

COPYRIGHT
       Copyright (c) 2001-2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>




log                                                  1.3                                              log(n)