What is Usage?
···
===========
Usage is simple way to access command line parameters for quick scripts that you write where you don't want to even think about command line processing. It handles many simple cases but does not have enough power to handle complicated option processing.
How can I get it?
gem install Usage
Where is it at?
http://raa.ruby-lang.org/project/usage/
Show me some examples
1. Simple Usage
The only thing you have remember to use usage are how commands are usually documented.
First you need to require the usage library:
require "Usage"
Then set up the usage string for the command:
usage = Usage.new "infile outfile"
The above would be a command with two require arguments: an input file and an output file.
To access those arguments, you just need to use the usage variable that was created and
send the .infile or .outfile message to them.
File.open(usage.infile) do |fi|
File.open(usage.outfile, "w") do |fo|
fo.write(fi.read)
end
end
If the user doesn't supply the correct number of arguments, the program exits with an error
and the usage for the program (hence the libraries name).
PROGRAM: test.rb
ERROR: too few arguments 2 expected, 0 given
USAGE: test.rb infile outfile
2. Lists of files (...)
You can write a program that accepts a list of files by using elipses appended to an
argument (the following program concatenates the input files into one output file).
usage = Usage.new "outfile infiles..."
File.open(usage.outfile, "w") do |fo|
usage.infiles.each do |infile|
File.open(usage.infile) { |fi| fo.write(fi.read)}
end
end
3. Optional arguments
You can have optional arguments by surounding them in square brackets.
usage = Usage.new "required_arg [optional_arg] "
These are accessed in the standard way
usage.optional_arg # this is nil if it is not given by the user
usage.required_arg
4. Options
You can have dash options that are either required or optional. Options can also have
arguments associated with them.
usage = Usage.new "[-y] [-x excluded_tags] (-z ztag) (-w warning_arg) files..."
The options are accessed with "dash_" prefixing the option so that the -y is accessed
via .dash_y. The -x can be accessed either with #dash_x (which would be either nil or
true) or #excluded_tags (which would be either nil or the argument for the -x option).
The -z option is required and has one argument, also the -w option is also required.
They can appear in any order (-z option first or -w option first). The optional arguments
can appear either before, interspersed with, or after the required options.
5. Long Options
You can also have long options by including lines following the initial usage line that
associates the short options with the long ones. Example below:
usage = Usage.new "-x files...", <<EOT
-x,--exclusive specifies exclusive access to the files
EOT
With this case, now #dash_x and #exclusive give the same result when applied to the usage
variable.
6. Typed options
In order to remove a step and improve argument checking, you can also add in a "type"
character to identify its type. The characters I used are somewhat arbitrary. Some of
them I took from BASIC which I programmed in long long ago.
% - Integer
$ - String (but this is unnecessary as this is default)
# - Float
@ - Date-Time
So when you send the argument message to the usage object, you will get a value of that
type and if the user does not give that type, then they get an error message.
usage = Usage.new "%num_times @on_date"
In this example, #num_times returns and Integer object and #on_date returns a Time object.
7. Choice options
You can have optional options that have a set of values which they can be. The choices
are separated by pipe symbols. See below:
usage = Usage.new "[-a coffee|tea|milk]"
After this #dash_a will give the string coffee, tea, or milk. If the value given isn't
one of the given choices, then the user is given an error message with the
appropriate choices.
Steve Tuckner
