log(n)								 Logging facility							    log(n)

NAME

       log - Procedures to log messages of libraries and applications.

SYNOPSIS

       package require Tcl 8

       package require log ?1.0.1?

       ::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::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::lvSupress 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  mes-
       sages of level notice are given to the non-standard command toText for logging. This disables the channel setting for such messages, assum-
       ing that toText does not use it by itself.

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

       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 applica-
       tion 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 mes-
	      sage 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  miscon-
	      figurations of the log facility or errors in the callers code itself.

       ::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

KEYWORDS

       log, log level, message level, message

log								       1.0.1								    log(n)