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Tag Archive for 'Library'
21Aug09 Arguments with Trollop
ruby rubygems
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At various points in my life, I’ve used many methods of parsing command line options, from rolling my own, to using getopt or other libraries.  Recently I came across a new one which has its own view of how to parse commandline arguments.

Trollop is, as they put it, “Yet Another Fine CommandLine Argument Parsing Library” (YAFCLAP).  It’s goal is to be as easy as possible.  You can install it as a single file in lib, or use it as a gem.  Trollop doesn’t care.  To install, you can download it from rubyforge, or use the ever popular:

  |  copy code |? 
1
gem install trollop

(you may need to prepend sudo, or run it as root).

Let’s take a look at a simple example:

  |  copy code |? 
01
require '<a class="zem_slink" title="RubyGems" rel="homepage" href="http://docs.rubygems.org">rubygems</a>'
02
require 'trollop'
03
opts = Trollop::options do
04
  opt :host, "Host to connect to", :default => "localhost"
05
  opt :port, "jmx remote port", :default => 4444
06
  opt :interval, "How often do we poll (in seconds)", :default => 10
07
  opt :count, "How many intervals, 0 == infinite, use ^C (SIGINT) to exit and write output", :default => 0
08
end
09
p opts
10

 

The first argument to opt is the name of the option.  We don’t have to specify a switch; it’s smart enough to figure out a mapping for them.  The second is a description of the argument.  You can specify a default value and/or a type.  In this example, we’ve specified defaults.  And here it is in use:

  |  copy code |? 
01
$ ruby trollop_simple.rb
02
{:interval=>10, :count=>0, :help=>false, :host=>"localhost", :port=>4444}
03
$ ruby trollop_simple.rb -h
04
Error: option '-h' needs a parameter.
05
Try --help for help.
06
$ ruby trollop_simple.rb --help
07
Options:
08
      --host, -h <s>:   Host to connect to (default: localhost)
09
      --port, -p <i>:   jmx remote port (default: 4444)
10
  --interval, -i <i>:   How often do we poll (in seconds) (default: 10)
11
     --count, -c <i>:   How many intervals, 0 == infinite, use ^C (SIGINT) to
12
                        exit and write output (default: 0)
13
          --help, -e:   Show this message
14
 
15
 
16

Notice that it has set up mappings for us as well as created a nicely formatted help — though it’s a default, without a lot of information.   Let’s add a version and usage:

  |  copy code |? 
01
require 'rubygems'
02
require 'trollop'
03
opts = Trollop::options do
04
  version <<EOF
05
jmx_mon -- we be jammin' with version zz9-za aka Arthur Dent
06
Don't forget your towel!
07
EOF
08
 
09
  banner <<EOF
10
jmx_mon is a program to monitor a jmx bean\'s value over time.
11
It can output the data as a csv, a graph in a pdf, or both.
12
 
13
Usage jmx_mon [options]
14
where [options] are:
15
EOF
16
  opt :host, "Host to connect to", :default => "localhost"
17
  opt :port, "jmx remote port", :default => 4444
18
  opt :interval, "How often do we poll (in seconds)", :default => 10
19
  opt :count, "How many intervals, 0 == infinite, use ^C (SIGINT) to exit and write output", :default => 0
20
end
21
p opts
22

Now let’s see what we have:

  |  copy code |? 
01
$ ruby trollop_simple.rb --help
02
jmx_mon is a program to monitor a jmx bean's value over time.
03
It can output the data as a csv, a graph in a pdf, or both.
04
 
05
Usage jmx_mon [options]
06
where [options] are:
07
      --host, -h <s>:   Host to connect to (default: localhost)
08
      --port, -p <i>:   jmx remote port (default: 4444)
09
  --interval, -i <i>:   How often do we poll (in seconds) (default: 10)
10
     --count, -c <i>:   How many intervals, 0 == infinite, use ^C (SIGINT) to
11
                        exit and write output (default: 0)
12
       --version, -v:   Print version and exit
13
          --help, -e:   Show this message
14
 
15
$ ruby trollop_simple.rb -v
16
jmx_mon -- we be jammin' with version zz9-za aka Arthur Dent
17
Don't forget your towel!
18
 
19

We now have a nicer usage, as well as version.  Also, it will stop automagickally if we ask for help or the version.

All of the options are placed in the opts hash; let’s see what we can do with it:

  |  copy code |? 
01
require 'rubygems'
02
require 'trollop'
03
 
04
aliases = {
05
      :MEMORY_HEAP => "Heap memory usage, multiple values",
06
      :MEMORY_HEAP_USED => "Used heap memory"
07
}
08
 
09
opts = Trollop::options do
10
  version <<EOF
11
jmx_mon -- we be jammin' with version zz9-za aka Arthur Dent
12
Don't forget your towel!
13
EOF
14
 
15
  banner <<EOF
16
jmx_mon is a program to monitor a jmx bean\'s value over time.
17
It can output the data as a csv, a graph in a pdf, or both.
18
 
19
Usage jmx_mon [options]
20
where [options] are:
21
EOF
22
  opt :host, "Host to connect to", :default => "localhost"
23
  opt :port, "jmx remote port", :default => 4444
24
  opt :interval, "How often do we poll (in seconds)", :default => 10
25
  opt :count, "How many intervals, 0 == infinite, use ^C (SIGINT) to exit and write output", :default => 0
26
  opt :aliases, "Print defined bean aliases & exit.", :default => false
27
  opt :towel, "Don't forget this!", :default => false
28
end
29
 
30
if opts[:aliases_given]
31
  aliases.each_pair do |key, value|
32
    puts "#{key}: #{value}"
33
  end
34
  exit
35
end
36
 
37
Trollop::die :towel, "You forgot your towel.  You've been eaten by a Ravenous Bugblatter Beast of Traal" unless opts[:towel]
38
 
39
p opts
40

We’ve added two more options, one for printing out aliases, and another indicating whether or not you have your towel — with deadly results should you forget.

  |  copy code |? 
1
$ ruby trollop_simple.rb -a    
2
MEMORY_HEAP: Heap memory usage, multiple values
3
MEMORY_HEAP_USED: Used heap memory
4
 
5
$ ruby trollop_simple.rb   
6
Error: argument --towel You forgot your towel.  You've been eaten by a Ravenous Bugblatter Beast of Traal.
7
Try --help for help.
8
 
9

There’s more that you can do with trollop; the website and documentation gives more examples.  However, I’d suggest considering trollop the next time you need to parse the command line.

 

 

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