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
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>