xail - tail for winners

xail is a super lightweight Ruby DSL for building simple stream/log analysis tools.

A simple log viewer: logview.xail.rb:

#!/usr/bin/env xail
group('fatal') {
    contains 'fatal'
    bell
}

group('error') {
    contains 'error', 'exception'
    red
    bold
}

group('warning') {
    contains 'warn'
    yellow
}

You can then run it directly:

$ ./logview.xail.rb

And it will accept input on stdin or a filename on the command line.

You can directly specify:

Filters

There are filters and compound filters. A filter takes a line from a stream and performs some action, potentially altering the stream, or terminating the flow. Compound filters take a stream and also a set of subfilters. These generally implement flow control.

Stdout is the ultimate consumer of the strings, unless they've been redirected using rest.

Compound Filters

• cascade -- stream the result of first subfilter that streams, a cascade filter is the container for your xail script

• composition -- applies each subfilter on the stream of the preceding subfilter, streaming the final result

• and -- streams the original if all subfilters stream

• or -- streams the original if any subfilter streams

• not -- streams the original if no subfilters stream

Matching Filters

• contains -- streams the original if any of the parameters are included
• replace -- mutates the stream

Alerting Filters

• execute executes a command, replacing {} with the line content
• bell rings a terminal bell (if possible)

Styling Filters

• black, red, green, yellow, blue, magenta, cyan, white -- adjust foreground color
• onblack, onred, ongreen, onyellow, onblue, onmagenta, oncyan, onwhite -- adjust background color
• bold, blink, underscore, negative, dark -- apply effects to the text

Special Filters

• sample -- samples the stream, only printing at the rate requested
• stop -- stops processing of this stream and continues with the next
• count -- [todo] computes the rate of the stream for display (need UI aspect)
• rest -- a special compound filter that is applied to any unmatched streams

Custom Filters

You can easily develop your own filters. Either as an anonymous block:

filter do |stream|
  if stream.includes? 'awesome'
    nil # stop the stream
  else
    stream # keep it going
  end
end

Or, if you need to preserve state, as a filter within the xail file:

class LineNumbersFilter < AbstractFilter
    def initialize
      @lineno = 0
    end

    def streamLine(line)
      @lineno += 1
      return "%5d %s" % [@lineno, line]
    end
end

linenumbers
group('fatal') {
    contains 'fatal'
    red
}

Hide unfiltered lines

By default xail will print any unfiltered lines as this is a more typical case. You can hide unfiltered lines using a rest block. For example, to only show exceptions:

group('error') {
  contains 'exception'
  red
}

stop

Fine-grained stream control

You can preform finer grained stream control using the OR, AND, and NOT combinators.