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.
- •
- 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.
KEYWORDS¶
log, log level, message, message level
CATEGORY¶
Programming tools
COPYRIGHT¶
Copyright (c) 2001-2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>