Provided by: tcllib_2.0+dfsg-2_all 
NAME
log - Procedures to log messages of libraries and applications.
SYNOPSIS
package require Tcl 8.5 9
package require log ?1.5?
::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::logsubst level msg
::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::logsubst level msg
Like ::log::log, but msg may contain substitutions and variable references, which are evaluated in
the caller scope first. The purpose of this command is to avoid overhead in the non-logging case,
if the log message building is expensive. Any substitution errors raise an error in the command
execution. The following example shows an xml text representation, which is only generated in
debug mode:
log::logsubst debug {XML of node $node is '[$node toXml]'}
::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.
• 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 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 Trackers [http://core.tcl.tk/tcllib/reportlist]. Please
also report any ideas for enhancements you may have for either package and/or documentation.
When proposing code changes, please provide unified diffs, i.e the output of diff -u.
Note further that attachments are strongly preferred over inlined patches. Attachments can be made by
going to the Edit form of the ticket immediately after its creation, and then using the left-most button
in the secondary navigation bar.
KEYWORDS
log, log level, message, message level
CATEGORY
Programming tools
COPYRIGHT
Copyright (c) 2001-2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>