log(3tcl) Logging facility log(3tcl)______________________________________________________________________________NAMElog - 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 associ‐
ated with a level determining the importance of the message. The user
can then select which levels to log, what commands to use for the log‐
ging of each level and the channel to write the message to. In the fol‐
lowing example the logging of all message with level debug is deacti‐
vated.
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 log‐
ging 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 log‐
ging. 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 lev‐
els 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 -com‐
mand 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 sup‐
pressed. 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 com‐
mand 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 hav‐
ing 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 sup‐
pressed the actual logging is delegated to the specified com‐
mand. 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 facil‐
ity 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 writ‐
ing 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.
· 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 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(3tcl)
