NAME
    log-defer-viz - command-line utility for rendering log messages created
    by Log::Defer

DESCRIPTION
    Log::Defer is a module that creates structured logs. The Log::Defer
    documentation explains structured logging and its benefits over ad-hoc
    logging.

    This module installs a command-line script that parses structured logs
    created by Log::Defer and displays them in a readable manner.

INSTALLATION
    The fastest way to install "log-defer-viz" is with cpanminus:

        curl -sL https://raw.github.com/miyagawa/cpanminus/master/cpanm | sudo perl - Log::Defer::Viz

SWITCHES
  INPUT METHODS
        $ cat file.log | log-defer-viz
        $ log-defer-viz < file.log
        $ log-defer-viz file.log
        $ log-defer-viz -f file.log # continuously tail file
        $ log-defer-viz file.log file2.log
        $ log-defer-viz archived.log.gz more_logs.bz2

  INPUT FORMAT
        $ log-defer-viz --input-format=json  ## default is newline separated JSON
        $ log-defer-viz --input-format=sereal  ## Sereal::Decoder (not impl)
        $ log-defer-viz --input-format=messagepack  ## Data::MessagePack (not impl)
        $ log-defer-viz --input-format=storable  ## Storable (not impl)

    Note: The only input format currently implemented is newline-separated
    JSON.

  LOG MESSAGES
        $ log-defer-viz  ## by default shows error, warn, and info logs
        $ log-defer-viz -v  ## verbose mode (adds debug logs and more)
        $ log-defer-viz --debug  ## show debug logs
        $ log-defer-viz --quiet  ## only errors and warnings
        $ log-defer-viz --verbosity 25  ## numeric verbosity threshold
        $ log-defer-viz --nowarn  ## muffle warn logs (so show error and info)
        $ log-defer-viz --nologs  ## don't show log section
        $ log-defer-viz --nocolour  ## turn off terminal colours
        $ log-defer-viz --preserve-newlines # don't indent multi-line log messages

  TIMERS
        $ log-defer-viz --timer-columns 80  ## width of timer chart
        $ log-defer-viz --since-now  ## show relative to now times
                                     ##   like "34 minutes ago"
        $ log-defer-viz --notimers  ## don't show timer chart
        $ log-defer-viz --tz UTC  ## show times in UTC, not local

  DATA SECTION
    Applications can optionally log information in a "data" hash. This
    information is mostly designed to be extracted by programs so
    "log-defer-viz" doesn't display it by default. Use the "--data" option
    to display it anyway, and the "--data-format" option to choose the
    format to display it in. The available formats are "pretty-json",
    "json", "yaml", and "dumper".

        $ log-defer-viz --data  ## show data section. default is pretty-json
        $ log-defer-viz --data-format=json  ## compact, not pretty
        $ log-defer-viz --data-format=dumper  ## Data::Dumper
        $ log-defer-viz --data-only  ## only show data

  FILTERS, TRANSFORMS, AGGREGATES
    As described in detail in their respective sections below, "--grep",
    "--map", and "--reduce" allow flexible selection and manipulation of
    your log data using arbitrary perl code. In the provided perl code, $_
    refers to the log entry as a hash-reference. In "--reduce" there is also
    a special $o output variable.

        $ log-defer-viz --grep '$_->{data}'  ## grep for records that have a data section.
                                             ## $_ is the entire Log::Defer entry.
        $ log-defer-viz --map '$_->{data}->{username}'  ## Extract username from data
        $ log-defer-viz --reduce '$o->{ $_->{data}->{ip_addr} }++'  ## Count IP addresses

  COUNT
    The count parameter tallies values found in log file. The arguments can
    be keys in the data section or arbitrary perl code. Multiple values are
    accepted. Note: This feature is mostly obsoleted by the "--reduce"
    feature but is kept for backwards compatibility and because it can be
    quite convenient.

        $ log-defer-viz --data --count ip_address ## display how many log lines for each ip address
        $ log-defer-viz --data --count ip_address --count '$_->{data}->{login_info}->{username}'

  MISCELLANEOUS
        $ log-defer-viz --help  ## the text you are reading now
        $ log-defer-viz --sort-time  ## sort by start time

GREPING
    As shown above, there is a "--grep" command-line option. This lets you
    filter log messages using arbitrary perl code. If the expression returns
    true, the log message is processed and displayed as usual.

    Being able to do this easily is an important advantage of structured
    logs. With unstructured logs it is often difficult to extract all of the
    information related to a request and nothing else.

    For example, here is how to grep for all requests that took longer than
    500 milliseconds:

        $ log-defer-viz --grep '$_->{end} > .5' server.log

    Depending on your underlying storage format, it may be meaningful to
    grep before passing to "log-defer-viz" (usually for performance
    reasons). Currently the only supported storage format is
    newline-separated JSON which *is* designed to be pre-grepable. If your
    search string appears anywhere in the object, the entire log message
    will be displayed:

        $ grep 10.9.1.2 app.log | log-defer-viz

    The final and most error-prone way to grep Log::Defer logs is to grep
    the unstructured output of "log-defer-viz" (not recommended):

        $ log-defer-viz app.log | grep 10.9.1.2

    In general, "--grep" can be combined with other switches that take
    expressions such as "--map" and "--reduce". In these cases, the greping
    will occur first.

MAPPING
    Similar to "--grep", there is also a "--map" command-line option. If
    this option is passed in, the only output is whatever your "--map"
    expression returns.

    For example, if you are putting the PID into the data section with
    "$log->data->{pid} = $$", then you can extract the PID like so:

        $ log-defer-viz --map '$_->{data}->{pid}' < app.log
        9765
        9768
        9771

    Join together fields with a pipe:

        $ log-defer-viz --map 'join "|", $_->{data}{pid}, $_->{start}' < app.log
        9765|1362166673.95104
        9768|1362168038.85611
        9771|1362169482.39561

    Make dates readable ("localtime" in scalar context makes a timestamp
    readable):

        $ log-defer-viz --map 'join "|", $_->{data}{pid}, "".localtime($_->{start})' < app.log
        9765|Fri Mar  1 14:37:53 2013
        9768|Fri Mar  1 15:00:38 2013
        9771|Fri Mar  1 15:24:42 2013

    As with "--grep", you have access to any perl functions you might need.
    Also, you can combine "--map" and "--grep". The grep filtering will be
    applied before the mapping.

    For example, here is how to do a "pass-through grep" where the output is
    another valid JSON-encoded Log::Defer file:

        $ export USER=jimmy
        $ log-defer-viz -g "_->{data}{username} eq '$USER'" \
                        -m "encode_json _"                  \
                        < requests.log                      \
                        > jimmys-requests.log

    Note that the above also demonstrates two shortcut features: First, the
    "-g" and "-m" switches are abbreviations for "--grep" and "--map"
    respectively. Second, in grep and map expressions the "_" function is an
    abbreviation for $_. Although this is one character shorter, the main
    reason this exists is so that you can use double-quoted strings without
    having to worry about escaping "$" characters from your shell.

REDUCING
    Unlike "--map" which outputs the same number of values that were input,
    and "--grep" that can return any number up to that amount, "--reduce"
    returns exactly one value.

    While the expression passed in as an argument to "--reduce" is being
    evaluated, there is a special variable called $o available. The initial
    value of this variable is an empty hash ("{}") and the value stored
    there is preserved across all invocations of your reduce expression.
    This means it can be used for counters and accumulators and such.

    The most straightforward use-case is the simple tally or count. For
    example, here is how you could mimic the (somewhat deprecated) "--count"
    feature and get the sum totals of the different HTTP status codes
    present in the log file:

        $ log-defer-viz --reduce '$o->{ $_->{data}->{status_code} }++' \
                        service.log
        {
            "200": 10293,
            "404": 392,
            "304": 3012,
            "500": 2
        }

    Here is how to count how many log entries contain at least one error
    message (log level 10 or lower, see Log::Defer):

        --reduce '$o->{errors}++ if grep { $_->[1] <= 10 } @{ $_->{logs} }'

    As with "--data" and "--count", the default output format is prettified
    JSON but you can change that with the "--data-format" option.

SEE ALSO
    Log::Defer

    Log::Defer::Viz github repo <https://github.com/hoytech/Log-Defer-Viz>

    The "log-defer-viz" is also useful for visualising logs created by
    Michael Pucyk's LogDefer Python module
    <https://github.com/mikep/LogDefer> (since it outputs the same format)

AUTHOR
    Doug Hoyte, "<doug@hcsw.org>"

CONTRIBUTORS
    Matt Phillips, "<mattp@cpan.org>"

    Mike P

    Mike R

    Avianna

    Thanks to the above and also to everyone else who has given feedback or
    suggestions.

COPYRIGHT & LICENSE
    Copyright 2013-2014 Doug Hoyte and contributors.

    This module is licensed under the same terms as perl itself.

