Related
I've spent a few hours searching for a way to push an array into another array or into a hash. Apologies in advance if the formatting of this question is bit messy. This is the first time I've asked a question on StackOverflow so I'm trying to get the hang of styling my questions properly.
I have to write some code to make the following test unit past:
class TestNAME < Test::Unit::TestCase
def test_directions()
assert_equal(Lexicon.scan("north"), [['direction', 'north']])
result = Lexicon.scan("north south east")
assert_equal(result, [['direction', 'north'],
['direction', 'south'],
['direction', 'east']])
end
end
The most simple thing I've come up with is below. The first part passes, but then the second part is not returning the expected result when I run rake test.
Instead or returning:
[["direction", "north"], ["direction", "south"], ["direction",
"east"]]
it's returning:
["north", "south", "east"]
Although, if I print the result of y as a string to the console, I get 3 separate arrays that are not contained within another array (as below). Why hasn't it printed the outermost square brackets of the array, y?
["direction", "north"]
["direction", "south"]
["direction", "east"]
Below is the code I've written in an attempt to pass the test unit above:
class Lexicon
def initialize(stuff)
#words = stuff.split
end
def self.scan(word)
if word.include?(' ')
broken_words = word.split
broken_words.each do |word|
x = ['direction']
x.push(word)
y = []
y.push(x)
end
else
return [['direction', word]]
end
end
end
Any feedback about this will be much appreciated. Thank you all so much in advance.
What you're seeing is the result of each, which returns the thing being iterated over, or in this case, broken_words. What you want is collect which returns the transformed values. Notice in your original, y is never used, it's just thrown out after being composed.
Here's a fixed up version:
class Lexicon
def initialize(stuff)
#words = stuff.split
end
def self.scan(word)
broken_words = word.split(/\s+/)
broken_words.collect do |word|
[ 'direction', word ]
end
end
end
It's worth noting a few things were changed here:
Splitting on an arbitrary number of spaces rather than one.
Simplifying to a single case instead of two.
Eliminating the redundant return statement.
One thing you might consider is using a data structure like { direction: word } instead. That makes referencing values a lot easier since you'd do entry[:direction] avoiding the ambiguous entry[1].
If you're not instantiating Lexicon objects, you can use a Module which may make it more clear that you're not instantiating objects.
Also, there is no need to use an extra variable (i.e. broken_words), and I prefer the { } block syntax over the do..end syntax for functional blocks vs. iterative blocks.
module Lexicon
def self.scan str
str.split.map {|word| [ 'direction', word ] }
end
end
UPDATE: based on Cary's comment (I assume he meant split when he said scan), I've removed the superfluous argument to split.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Is there a `pipe` equivalent in ruby?
I'm looking at the tap method in Ruby - but unfortunately the object returned from the passed block is not passed on. What method do I use to have the object passed on?
Here's what I'm trying to (unsuccessfully) do:
obj.tap{ |o| first_transform(o) }.tap{ |o| second_transform(o)}
This is, of course, equivalent to second_transform(first_transform(o)). I'm just asking how to do it the first way.
Doing this is trivial with lists:
list.map{ |item| first_transform(item) }.map{ |item| second_transform(item)}
Why isn't it as easy with objects?
class Object
def as
yield self
end
end
With this, you can do [1,2,3].as{|l| l << 4}.as{|l| l << 5}
You could also consider to make #first_transform and #second_transform instance methods of the item's class (and return the transformed item of course).
These methods definitions should look like this:
class ItemClass
# If you want your method to modify the object you should
# add a bang at the end of the method name: first_transform!
def first_transform
# ... Manipulate the item (self) then return it
transformed_item
end
end
This way you could simply chain the methods calls this way:
list.map {|item| item.first_transform.second_transform }
It even reads better in my humble opinion ;)
The simple answer is tap doesn't do what you think it does.
tap is called on an object and will always return that same object.
As a simple example of taps use
"foo".tap do |foo|
bar(foo)
end
This still returns "foo"
In your example you have an object, and you want to apply two functions to it in succession.
second_transform(first_transform(obj))
UPDATED:
So I guess I'd ask why you want to chain in this way.
obj.do{|o| first_transform(o)}.do{|o| second_transform(o)}
Is that really more clear than
second_transform(first_transform(obj))
Lets take an example I often use
markdown(truncate(#post.content))
or
truncated_post = truncate(#post.content)
markdown(truncated_post)
I guess it depends on the nature of your transform
When programming ruby I always find myself doing this:
a = [a, b].min
This means compare a and b and store the smallest value in a. I don't like writing the code above as I have to write a twice.
I know that some non-standard dialects of C++ had an operator which did exactly this
a <?= b
Which I find very convenient. But I'm not really interested in the operator as much as I'm in the feature of avoiding repetition. I would also be happy if I could write
a.keep_max(b)
a can be a quite long variable, like my_array[indice1][indice2], and you don't want to write that twice.
I did alot of googling on this and found no result, hopefully this question will pop up and be useful for others aswell.
So, is there any non-repeitive way to express what I want in ruby?
What you would like to do is in fact not possible in ruby (see this question). I think the best you can do is
def max(*args)
args.max
end
a = max a, b
I don't understand your question. You can always do something like this ...
module Comparable
def keep_min(other)
(self <=> other) <= 0 ? self : other
end
def keep_max(other)
(self <=> other) >= 0 ? self : other
end
end
1.keep_min(2)
=> 1
1.keep_max(2)
=> 2
Well, that won't work for all objects with <=> because not all of them are implementing Comparable, so you could monkey-patch Object.
Personally I prefer clarity and tend to avoid monkey-patching. Plus, this clearly is a binary predicate, just like "+", therefore method-chaining doesn't necessarily make sense so I prefer something like this to get rid of that array syntax:
def min(*args)
args.min
end
def max(*args)
args.max
end
min(1, 2)
=> 1
max(1, 2)
=> 2
But hey, I'm also a Python developer :-)
You can define your own method for it:
class Object
def keep_max(other)
[self, other].max
end
end
a = 3
b = 7
puts a.keep_max(b)
But you should be careful defining methods on Object as it can have unpredictable behaviour (for example, if objects cannot be compared).
def keep_max(var, other, binding)
eval "#{var} = [#{var}, #{other}].max", binding
end
a = 5
b = 78
keep_max(:a, :b, binding)
puts a
#=> 78
This basically does what you want. Take a look at Change variable passed in a method
I'm not entirely sure if this is possible in Ruby, but hopefully there's an easy way to do this. I want to declare a variable and later find out the name of the variable. That is, for this simple snippet:
foo = ["goo", "baz"]
How can I get the name of the array (here, "foo") back? If it is indeed possible, does this work on any variable (e.g., scalars, hashes, etc.)?
Edit: Here's what I'm basically trying to do. I'm writing a SOAP server that wraps around a class with three important variables, and the validation code is essentially this:
[foo, goo, bar].each { |param|
if param.class != Array
puts "param_name wasn't an Array. It was a/an #{param.class}"
return "Error: param_name wasn't an Array"
end
}
My question is then: Can I replace the instances of 'param_name' with foo, goo, or bar? These objects are all Arrays, so the answers I've received so far don't seem to work (with the exception of re-engineering the whole thing ala dbr's answer)
What if you turn your problem around? Instead of trying to get names from variables, get the variables from the names:
["foo", "goo", "bar"].each { |param_name|
param = eval(param_name)
if param.class != Array
puts "#{param_name} wasn't an Array. It was a/an #{param.class}"
return "Error: #{param_name} wasn't an Array"
end
}
If there were a chance of one the variables not being defined at all (as opposed to not being an array), you would want to add "rescue nil" to the end of the "param = ..." line to keep the eval from throwing an exception...
You need to re-architect your solution. Even if you could do it (you can't), the question simply doesn't have a reasonable answer.
Imagine a get_name method.
a = 1
get_name(a)
Everyone could probably agree this should return 'a'
b = a
get_name(b)
Should it return 'b', or 'a', or an array containing both?
[b,a].each do |arg|
get_name(arg)
end
Should it return 'arg', 'b', or 'a' ?
def do_stuff( arg )
get_name(arg)
do
do_stuff(b)
Should it return 'arg', 'b', or 'a', or maybe the array of all of them? Even if it did return an array, what would the order be and how would I know how to interpret the results?
The answer to all of the questions above is "It depends on the particular thing I want at the time." I'm not sure how you could solve that problem for Ruby.
It seems you are trying to solve a problem that has a far easier solution..
Why not just store the data in a hash? If you do..
data_container = {'foo' => ['goo', 'baz']}
..it is then utterly trivial to get the 'foo' name.
That said, you've not given any context to the problem, so there may be a reason you can't do this..
[edit] After clarification, I see the issue, but I don't think this is the problem.. With [foo, bar, bla], it's equivalent like saying ['content 1', 'content 2', 'etc']. The actual variables name is (or rather, should be) utterly irrelevant. If the name of the variable is important, that is exactly why hashes exist.
The problem isn't with iterating over [foo, bar] etc, it's the fundamental problem with how the SOAP server is returing the data, and/or how you're trying to use it.
The solution, I would say, is to either make the SOAP server return hashes, or, since you know there is always going to be three elements, can you not do something like..
{"foo" => foo, "goo" => goo, "bar"=>bar}.each do |param_name, param|
if param.class != Array
puts "#{param_name} wasn't an Array. It was a/an #{param.class}"
puts "Error: #{param_name} wasn't an Array"
end
end
OK, it DOES work in instance methods, too, and, based on your specific requirement (the one you put in the comment), you could do this:
local_variables.each do |var|
puts var if (eval(var).class != Fixnum)
end
Just replace Fixnum with your specific type checking.
I do not know of any way to get a local variable name. But, you can use the instance_variables method, this will return an array of all the instance variable names in the object.
Simple call:
object.instance_variables
or
self.instance_variables
to get an array of all instance variable names.
Building on joshmsmoore, something like this would probably do it:
# Returns the first instance variable whose value == x
# Returns nil if no name maps to the given value
def instance_variable_name_for(x)
self.instance_variables.find do |var|
x == self.instance_variable_get(var)
end
end
There's Kernel::local_variables, but I'm not sure that this will work for a method's local vars, and I don't know that you can manipulate it in such a way as to do what you wish to acheive.
Great question. I fully understand your motivation. Let me start by noting, that there are certain kinds of special objects, that, under certain circumstances, have knowledge of the variable, to which they have been assigned. These special objects are eg. Module instances, Class instances and Struct instances:
Dog = Class.new
Dog.name # Dog
The catch is, that this works only when the variable, to which the assignment is performed, is a constant. (We all know that Ruby constants are nothing more than emotionally sensitive variables.) Thus:
x = Module.new # creating an anonymous module
x.name #=> nil # the module does not know that it has been assigned to x
Animal = x # but will notice once we assign it to a constant
x.name #=> "Animal"
This behavior of objects being aware to which variables they have been assigned, is commonly called constant magic (because it is limited to constants). But this highly desirable constant magic only works for certain objects:
Rover = Dog.new
Rover.name #=> raises NoMethodError
Fortunately, I have written a gem y_support/name_magic, that takes care of this for you:
# first, gem install y_support
require 'y_support/name_magic'
class Cat
include NameMagic
end
The fact, that this only works with constants (ie. variables starting with a capital letter) is not such a big limitation. In fact, it gives you freedom to name or not to name your objects at will:
tmp = Cat.new # nameless kitty
tmp.name #=> nil
Josie = tmp # by assigning to a constant, we name the kitty Josie
tmp.name #=> :Josie
Unfortunately, this will not work with array literals, because they are internally constructed without using #new method, on which NameMagic relies. Therefore, to achieve what you want to, you will have to subclass Array:
require 'y_support/name_magic'
class MyArr < Array
include NameMagic
end
foo = MyArr.new ["goo", "baz"] # not named yet
foo.name #=> nil
Foo = foo # but assignment to a constant is noticed
foo.name #=> :Foo
# You can even list the instances
MyArr.instances #=> [["goo", "baz"]]
MyArr.instance_names #=> [:Foo]
# Get an instance by name:
MyArr.instance "Foo" #=> ["goo", "baz"]
MyArr.instance :Foo #=> ["goo", "baz"]
# Rename it:
Foo.name = "Quux"
Foo.name #=> :Quux
# Or forget the name again:
MyArr.forget :Quux
Foo.name #=> nil
# In addition, you can name the object upon creation even without assignment
u = MyArr.new [1, 2], name: :Pair
u.name #=> :Pair
v = MyArr.new [1, 2, 3], ɴ: :Trinity
v.name #=> :Trinity
I achieved the constant magic-imitating behavior by searching all the constants in all the namespaces of the current Ruby object space. This wastes a fraction of second, but since the search is performed only once, there is no performance penalty once the object figures out its name. In the future, Ruby core team has promised const_assigned hook.
You can't, you need to go back to the drawing board and re-engineer your solution.
Foo is only a location to hold a pointer to the data. The data has no knowledge of what points at it. In Smalltalk systems you could ask the VM for all pointers to an object, but that would only get you the object that contained the foo variable, not foo itself. There is no real way to reference a vaiable in Ruby. As mentioned by one answer you can stil place a tag in the data that references where it came from or such, but generally that is not a good apporach to most problems. You can use a hash to receive the values in the first place, or use a hash to pass to your loop so you know the argument name for validation purposes as in DBR's answer.
The closest thing to a real answer to you question is to use the Enumerable method each_with_index instead of each, thusly:
my_array = [foo, baz, bar]
my_array.each_with_index do |item, index|
if item.class != Array
puts "#{my_array[index]} wasn't an Array. It was a/an #{item.class}"
end
end
I removed the return statement from the block you were passing to each/each_with_index because it didn't do/mean anything. Each and each_with_index both return the array on which they were operating.
There's also something about scope in blocks worth noting here: if you've defined a variable outside of the block, it will be available within it. In other words, you could refer to foo, bar, and baz directly inside the block. The converse is not true: variables that you create for the first time inside the block will not be available outside of it.
Finally, the do/end syntax is preferred for multi-line blocks, but that's simply a matter of style, though it is universal in ruby code of any recent vintage.
Locked. This question and its answers are locked because the question is off-topic but has historical significance. It is not currently accepting new answers or interactions.
Continuing the "Hidden features of ..." meme, let's share the lesser-known but useful features of Ruby programming language.
Try to limit this discussion with core Ruby, without any Ruby on Rails stuff.
See also:
Hidden features of C#
Hidden features of Java
Hidden features of JavaScript
Hidden features of Ruby on Rails
Hidden features of Python
(Please, just one hidden feature per answer.)
Thank you
From Ruby 1.9 Proc#=== is an alias to Proc#call, which means Proc objects can be used in case statements like so:
def multiple_of(factor)
Proc.new{|product| product.modulo(factor).zero?}
end
case number
when multiple_of(3)
puts "Multiple of 3"
when multiple_of(7)
puts "Multiple of 7"
end
Peter Cooper has a good list of Ruby tricks. Perhaps my favorite of his is allowing both single items and collections to be enumerated. (That is, treat a non-collection object as a collection containing just that object.) It looks like this:
[*items].each do |item|
# ...
end
Don't know how hidden this is, but I've found it useful when needing to make a Hash out of a one-dimensional array:
fruit = ["apple","red","banana","yellow"]
=> ["apple", "red", "banana", "yellow"]
Hash[*fruit]
=> {"apple"=>"red", "banana"=>"yellow"}
One trick I like is to use the splat (*) expander on objects other than Arrays. Here's an example on a regular expression match:
match, text, number = *"Something 981".match(/([A-z]*) ([0-9]*)/)
Other examples include:
a, b, c = *('A'..'Z')
Job = Struct.new(:name, :occupation)
tom = Job.new("Tom", "Developer")
name, occupation = *tom
Wow, no one mentioned the flip flop operator:
1.upto(100) do |i|
puts i if (i == 3)..(i == 15)
end
One of the cool things about ruby is that you can call methods and run code in places other languages would frown upon, such as in method or class definitions.
For instance, to create a class that has an unknown superclass until run time, i.e. is random, you could do the following:
class RandomSubclass < [Array, Hash, String, Fixnum, Float, TrueClass].sample
end
RandomSubclass.superclass # could output one of 6 different classes.
This uses the 1.9 Array#sample method (in 1.8.7-only, see Array#choice), and the example is pretty contrived but you can see the power here.
Another cool example is the ability to put default parameter values that are non fixed (like other languages often demand):
def do_something_at(something, at = Time.now)
# ...
end
Of course the problem with the first example is that it is evaluated at definition time, not call time. So, once a superclass has been chosen, it stays that superclass for the remainder of the program.
However, in the second example, each time you call do_something_at, the at variable will be the time that the method was called (well, very very close to it)
Another tiny feature - convert a Fixnum into any base up to 36:
>> 1234567890.to_s(2)
=> "1001001100101100000001011010010"
>> 1234567890.to_s(8)
=> "11145401322"
>> 1234567890.to_s(16)
=> "499602d2"
>> 1234567890.to_s(24)
=> "6b1230i"
>> 1234567890.to_s(36)
=> "kf12oi"
And as Huw Walters has commented, converting the other way is just as simple:
>> "kf12oi".to_i(36)
=> 1234567890
Hashes with default values! An array in this case.
parties = Hash.new {|hash, key| hash[key] = [] }
parties["Summer party"]
# => []
parties["Summer party"] << "Joe"
parties["Other party"] << "Jane"
Very useful in metaprogramming.
Another fun addition in 1.9 Proc functionality is Proc#curry which allows you to turn a Proc accepting n arguments into one accepting n-1. Here it is combined with the Proc#=== tip I mentioned above:
it_is_day_of_week = lambda{ |day_of_week, date| date.wday == day_of_week }
it_is_saturday = it_is_day_of_week.curry[6]
it_is_sunday = it_is_day_of_week.curry[0]
case Time.now
when it_is_saturday
puts "Saturday!"
when it_is_sunday
puts "Sunday!"
else
puts "Not the weekend"
end
Download Ruby 1.9 source, and issue make golf, then you can do things like this:
make golf
./goruby -e 'h'
# => Hello, world!
./goruby -e 'p St'
# => StandardError
./goruby -e 'p 1.tf'
# => 1.0
./goruby19 -e 'p Fil.exp(".")'
"/home/manveru/pkgbuilds/ruby-svn/src/trunk"
Read the golf_prelude.c for more neat things hiding away.
Boolean operators on non boolean values.
&& and ||
Both return the value of the last expression evaluated.
Which is why the ||= will update the variable with the value returned expression on the right side if the variable is undefined. This is not explicitly documented, but common knowledge.
However the &&= isn't quite so widely known about.
string &&= string + "suffix"
is equivalent to
if string
string = string + "suffix"
end
It's very handy for destructive operations that should not proceed if the variable is undefined.
The Symbol#to_proc function that Rails provides is really cool.
Instead of
Employee.collect { |emp| emp.name }
You can write:
Employee.collect(&:name)
One final one - in ruby you can use any character you want to delimit strings. Take the following code:
message = "My message"
contrived_example = "<div id=\"contrived\">#{message}</div>"
If you don't want to escape the double-quotes within the string, you can simply use a different delimiter:
contrived_example = %{<div id="contrived-example">#{message}</div>}
contrived_example = %[<div id="contrived-example">#{message}</div>]
As well as avoiding having to escape delimiters, you can use these delimiters for nicer multiline strings:
sql = %{
SELECT strings
FROM complicated_table
WHERE complicated_condition = '1'
}
Use a Range object as an infinite lazy list:
Inf = 1.0 / 0
(1..Inf).take(5) #=> [1, 2, 3, 4, 5]
More info here: http://banisterfiend.wordpress.com/2009/10/02/wtf-infinite-ranges-in-ruby/
I find using the define_method command to dynamically generate methods to be quite interesting and not as well known. For example:
((0..9).each do |n|
define_method "press_#{n}" do
#number = #number.to_i * 10 + n
end
end
The above code uses the 'define_method' command to dynamically create the methods "press1" through "press9." Rather then typing all 10 methods which essentailly contain the same code, the define method command is used to generate these methods on the fly as needed.
module_function
Module methods that are declared as module_function will create copies of themselves as private instance methods in the class that includes the Module:
module M
def not!
'not!'
end
module_function :not!
end
class C
include M
def fun
not!
end
end
M.not! # => 'not!
C.new.fun # => 'not!'
C.new.not! # => NoMethodError: private method `not!' called for #<C:0x1261a00>
If you use module_function without any arguments, then any module methods that comes after the module_function statement will automatically become module_functions themselves.
module M
module_function
def not!
'not!'
end
def yea!
'yea!'
end
end
class C
include M
def fun
not! + ' ' + yea!
end
end
M.not! # => 'not!'
M.yea! # => 'yea!'
C.new.fun # => 'not! yea!'
Short inject, like such:
Sum of range:
(1..10).inject(:+)
=> 55
Warning: this item was voted #1 Most Horrendous Hack of 2008, so use with care. Actually, avoid it like the plague, but it is most certainly Hidden Ruby.
Superators Add New Operators to Ruby
Ever want a super-secret handshake operator for some unique operation in your code? Like playing code golf? Try operators like
-~+~-
or
<---
That last one is used in the examples for reversing the order of an item.
I have nothing to do with the Superators Project beyond admiring it.
I'm late to the party, but:
You can easily take two equal-length arrays and turn them into a hash with one array supplying the keys and the other the values:
a = [:x, :y, :z]
b = [123, 456, 789]
Hash[a.zip(b)]
# => { :x => 123, :y => 456, :z => 789 }
(This works because Array#zip "zips" up the values from the two arrays:
a.zip(b) # => [[:x, 123], [:y, 456], [:z, 789]]
And Hash[] can take just such an array. I've seen people do this as well:
Hash[*a.zip(b).flatten] # unnecessary!
Which yields the same result, but the splat and flatten are wholly unnecessary--perhaps they weren't in the past?)
Auto-vivifying hashes in Ruby
def cnh # silly name "create nested hash"
Hash.new {|h,k| h[k] = Hash.new(&h.default_proc)}
end
my_hash = cnh
my_hash[1][2][3] = 4
my_hash # => { 1 => { 2 => { 3 =>4 } } }
This can just be damn handy.
Destructuring an Array
(a, b), c, d = [ [:a, :b ], :c, [:d1, :d2] ]
Where:
a #=> :a
b #=> :b
c #=> :c
d #=> [:d1, :d2]
Using this technique we can use simple assignment to get the exact values we want out of nested array of any depth.
Class.new()
Create a new class at run time. The argument can be a class to derive from, and the block is the class body. You might also want to look at const_set/const_get/const_defined? to get your new class properly registered, so that inspect prints out a name instead of a number.
Not something you need every day, but quite handy when you do.
create an array of consecutive numbers:
x = [*0..5]
sets x to [0, 1, 2, 3, 4, 5]
A lot of the magic you see in Rubyland has to do with metaprogramming, which is simply writing code that writes code for you. Ruby's attr_accessor, attr_reader, and attr_writer are all simple metaprogramming, in that they create two methods in one line, following a standard pattern. Rails does a whole lot of metaprogramming with their relationship-management methods like has_one and belongs_to.
But it's pretty simple to create your own metaprogramming tricks using class_eval to execute dynamically-written code.
The following example allows a wrapper object to forwards certain methods along to an internal object:
class Wrapper
attr_accessor :internal
def self.forwards(*methods)
methods.each do |method|
define_method method do |*arguments, &block|
internal.send method, *arguments, &block
end
end
end
forwards :to_i, :length, :split
end
w = Wrapper.new
w.internal = "12 13 14"
w.to_i # => 12
w.length # => 8
w.split('1') # => ["", "2 ", "3 ", "4"]
The method Wrapper.forwards takes symbols for the names of methods and stores them in the methods array. Then, for each of those given, we use define_method to create a new method whose job it is to send the message along, including all arguments and blocks.
A great resource for metaprogramming issues is Why the Lucky Stiff's "Seeing Metaprogramming Clearly".
use anything that responds to ===(obj) for case comparisons:
case foo
when /baz/
do_something_with_the_string_matching_baz
when 12..15
do_something_with_the_integer_between_12_and_15
when lambda { |x| x % 5 == 0 }
# only works in Ruby 1.9 or if you alias Proc#call as Proc#===
do_something_with_the_integer_that_is_a_multiple_of_5
when Bar
do_something_with_the_instance_of_Bar
when some_object
do_something_with_the_thing_that_matches_some_object
end
Module (and thus Class), Regexp, Date, and many other classes define an instance method :===(other), and can all be used.
Thanks to Farrel for the reminder of Proc#call being aliased as Proc#=== in Ruby 1.9.
The "ruby" binary (at least MRI's) supports a lot of the switches that made perl one-liners quite popular.
Significant ones:
-n Sets up an outer loop with just "gets" - which magically works with given filename or STDIN, setting each read line in $_
-p Similar to -n but with an automatic puts at the end of each loop iteration
-a Automatic call to .split on each input line, stored in $F
-i In-place edit input files
-l Automatic call to .chomp on input
-e Execute a piece of code
-c Check source code
-w With warnings
Some examples:
# Print each line with its number:
ruby -ne 'print($., ": ", $_)' < /etc/irbrc
# Print each line reversed:
ruby -lne 'puts $_.reverse' < /etc/irbrc
# Print the second column from an input CSV (dumb - no balanced quote support etc):
ruby -F, -ane 'puts $F[1]' < /etc/irbrc
# Print lines that contain "eat"
ruby -ne 'puts $_ if /eat/i' < /etc/irbrc
# Same as above:
ruby -pe 'next unless /eat/i' < /etc/irbrc
# Pass-through (like cat, but with possible line-end munging):
ruby -p -e '' < /etc/irbrc
# Uppercase all input:
ruby -p -e '$_.upcase!' < /etc/irbrc
# Same as above, but actually write to the input file, and make a backup first with extension .bak - Notice that inplace edit REQUIRES input files, not an input STDIN:
ruby -i.bak -p -e '$_.upcase!' /etc/irbrc
Feel free to google "ruby one-liners" and "perl one-liners" for tons more usable and practical examples. It essentially allows you to use ruby as a fairly powerful replacement to awk and sed.
The send() method is a general-purpose method that can be used on any Class or Object in Ruby. If not overridden, send() accepts a string and calls the name of the method whose string it is passed. For example, if the user clicks the “Clr” button, the ‘press_clear’ string will be sent to the send() method and the ‘press_clear’ method will be called. The send() method allows for a fun and dynamic way to call functions in Ruby.
%w(7 8 9 / 4 5 6 * 1 2 3 - 0 Clr = +).each do |btn|
button btn, :width => 46, :height => 46 do
method = case btn
when /[0-9]/: 'press_'+btn
when 'Clr': 'press_clear'
when '=': 'press_equals'
when '+': 'press_add'
when '-': 'press_sub'
when '*': 'press_times'
when '/': 'press_div'
end
number.send(method)
number_field.replace strong(number)
end
end
I talk more about this feature in Blogging Shoes: The Simple-Calc Application
Fool some class or module telling it has required something that it really hasn't required:
$" << "something"
This is useful for example when requiring A that in turns requires B but we don't need B in our code (and A won't use it either through our code):
For example, Backgroundrb's bdrb_test_helper requires 'test/spec', but you don't use it at all, so in your code:
$" << "test/spec"
require File.join(File.dirname(__FILE__) + "/../bdrb_test_helper")
Defining a method that accepts any number of parameters and just discards them all
def hello(*)
super
puts "hello!"
end
The above hello method only needs to puts "hello" on the screen and call super - but since the superclass hello defines parameters it has to as well - however since it doesn't actually need to use the parameters itself - it doesn't have to give them a name.
private unless Rails.env == 'test'
# e.g. a bundle of methods you want to test directly
Looks like a cool and (in some cases) nice/useful hack/feature of Ruby.