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 information 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 logging 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 standard
       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 convenience 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 command 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 message 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 facility 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
              suppressed the actual logging is delegated to the specified
              command. If there is no command specified 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, abbreviations
              are not allowed.

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

       o      emergency

       o      alert

       o      critical

       o      error

       o      warning

       o      notice

       o      info

       o      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 people 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://sourceforge.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)
