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ActiveTcl User Guide
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log(n) 1.2 "Logging facility"
log - Procedures to log messages of libraries and
applications.
TABLE OF
CONTENTS
SYNOPSIS
DESCRIPTION
API
LEVELS
KEYWORDS
COPYRIGHT
package require Tcl 8
package require log ?1.2?
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
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package require log
log::log notice "Some message"
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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.
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package require log
log::lvSuppress debug
log::log debug "Unseen message" ; # No output
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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.
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package require log
log::lvChannel debug stderr
log::log debug "Written to stderr"
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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.
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package require log
log::lvCmd notice toText
log::log notice "Handled by \"toText\""
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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.
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.
The package currently defines the following log levels, the
level of highest importance listed first.
- emergency
- alert
- critical
- error
- warning
- notice
- info
- debug
log , log level , message , message level
Copyright © 2001-2002 Andreas Kupries
<andreas_kupries@users.sourceforge.net>