My simple attempt to redefine instance methods are not working
class File
alias_method :old_atime, :atime
def atime(*args)
puts "helllllo"
old_atime(*args)
end
end
f = File.new("C:\\abc.txt","w")
puts f.atime
Any idea why?
I'm attempting to print "helllllo" everytime File#atime is called. Even alias old_atime atime is not working.
Is there something I'm doing wrong here?
Above code works perfectly as it should be. Puts "helllllo" writes "helllllo" in to your opened file. Puts inside the file instance meant for writing.
Just call f.close and open your file in text editor. You can see the content.
Yep, Ramesh is right. Try this:
class File
alias_method :old_atime, :atime
def atime(*args)
Kernel.puts "helllllo" # <---- Kernel method
old_atime(*args)
end
end
f = File.new("C:\\abc.txt","w")
puts f.atime
The issue is that 'puts' is defined in File for writing to files. You want the Kernel one which is used unless defined in a more specific scope.
This should work fine, but IO#puts writes to the IO object itself, not STDOUT. In other words, it's writing to the file.
Call f.atime a few times and then f.close within irb and you should see it printing helllllo to the file for each call to atime.
To print to STDOUT, you could use $stdout.puts or Kernel.puts.
Related
I wrote a basic ruby program with TextMate in Mac OS:
def hello
puts " This works!"
end
name it Check-it.rb
I open a Terminal session, cd to the directory where the program is stored.
Then I type
ruby Check-it.rb
And nothing appears.
ruby -v
shows me the version, so it's there.
But with this and every other Ruby program, nothing appears.
As others already pointed out. The code in your file
def hello
puts " This works!"
end
defines a method called hello that outputs a string. But that method is never called. To actually call that method and run it change your code in the file to
def hello # this block defines the `hello` method
puts " This works!"
end
hello # this line calls the method `hello`
I think you are not calling this method at all. Call this method and then run your code, it will work.
I am writing to a file instance. While the program is still running, the file is always empty. When I check the file after the script has executed, the file has content.
class A
def initialize
#file_ref=File.new("/user/shared/ruby/ruby-example/test.html","w+")
end
def fill
#file_ref.write("whatever\nwhatever\nwhatever\n")
end
end
The Main script:
require_relative 'A'
a=A.new
a.fill
puts File.size("/user/shared/ruby/ruby-example/test.html")
After the A instance has done its job, the puts statement will print "0" as if the file is empty. Indeed it is during program execution, but if I start irb:
puts File.size("/user/shared/ruby/ruby-example/test.html")
# => 27
$ cat test.html
whatever
whatever
whatever
Is my code wrong?
Is it normal that streams are flushed only after the execution of a process?
Ruby flushes IO buffers when you call IO#close or IO#flush. Since you are not calling neither close nor flush the buffers are flushed when the program terminates and the opened file descriptors are released.
Given your simple example a possible solution is:
class A
def initialize
#file_ref_name = '/user/shared/ruby/ruby-example/test.html'
end
def fill
File.open(#file_ref_name, 'w+') do |file|
file.write("whatever\nwhatever\nwhatever\n")
end
end
end
Passing a block to IO#open makes the opened file (the file variable in this example) to be closed (and therefore flushed) once the execution of the block terminates.
Please note that Ruby (to my knowledge since version 1.9) features a one liner shortcut for simple file writes as well, flush included:
File.write('/path/to/file.txt', 'content')
I'm new to Ruby, so apologies if this sounds really silly.
I can't seem to figure out how to write a "main" code and have methods in the same file (similar to C). I end up with a "main" file which loads a seperate file that has all the methods. I appreciate any guidance on this.
I spotted the following SO post but I don't understand it:
Should I define a main method in my ruby scripts?
While it's not a big deal, it's just easier being able to see all the relevant code in the same file. Thank you.
[-EDIT-]
Thanks to everyone who responded - turns out you just need to define all the methods above the code. An example is below:
def callTest1
puts "in test 1"
end
def callTest2
puts "in test 2"
end
callTest1
callTest2
I think this makes sense as Ruby needs to know all methods beforehand. This is unlike C where there is a header file which clearly list the available functions and therefore, can define them beneath the main() function
Again, thanks to everyone who responded.
#Hauleth's answer is correct: there is no main method or structure in Ruby. I just want to provide a slightly different view here along with some explanation.
When you execute ruby somefile.rb, Ruby executes all of the code in somefile.rb. So if you have a very small project and want it to be self-contained in a single file, there's absolutely nothing wrong with doing something like this:
# somefile.rb
class MyClass
def say_hello
puts "Hello World"
end
end
def another_hello
puts "Hello World (from a method)"
end
c = MyClass.new
c.say_hello
another_hello
It's not that the first two blocks aren't executed, it's just that you don't see the effects until you actually use the corresponding class/method.
The if __FILE__ == $0 bit is just a way to block off code that you only want to run if this file is being run directly from the command line. __FILE__
is the name of the current file, $0 is the command that was executed by the shell (though it's smart enough to drop the ruby), so comparing the two tells you precisely that: is this the file that was executed from the command line? This is sometimes done by coders who want to define a class/module in a file and also provide a command-line utility that uses it. IMHO that's not very good project structure, but just like anything there are use cases where doing it makes perfect sense.
If you want to be able to execute your code directly, you can add a shebang line
#!/usr/bin/env ruby
# rest of somefile.rb
and make it executable with chmod +x somefile.rb (optionally rename it without the .rb extension). This doesn't really change your situation. The if __FILE__ == $0 still works and still probably isn't necessary.
Edit
As #steenslag correctly points out, the top-level scope in Ruby is an Object called main. It has slightly funky behavior, though:
irb
>> self
=> main
>> self.class
=> Object
>> main
NameError: undefined local variable or method `main' for main:Object
from (irb):8
Don't worry about this until you start to dig much deeper into the language. If you do want to learn lots more about this kind of stuff, Metaprogramming Ruby is a great read :)
No there isn't such structure. Of course you can define main function but it won't be called until you do so. Ruby execute line by line so if you want to print 'Hello World' you simply write:
puts 'Hello World'
The question that you mentioned is about using one file as module and executable, so if you write
if __FILE__ == $0
# your code
end
It will be called only if you run this file. If you only require it in other file then this code will never run. But IMHO it's bad idea, better option is using RubyGems and there add executables.
Actually there is a main, but it is not a method; it's the top-level object that is the initial execution context of a Ruby program.
class Foo
p self
end
#=> Foo
p self
#=> main
def foo
p self
end
foo
#=> main
There is no magic main function in Ruby. See http://en.wikipedia.org/wiki/Main_function#Ruby
If you wish to run Ruby scripts like C compiled files, do the following:
#!/usr/bin/env ruby
puts "Hello"
and then chmod a+x file_name.rb. Everything that is below the first line will be run, as if it was contents of main in C. Of course class and function definitions won't give you any results until they are instantiated/invoked (although the code inside class definitions is actually evaluated, so you could get some output but this is not expected in normal circumstances).
Another way to write main() method is:
class HelloWorld
def initialize(name)
#name = name
end
def sayHello()
print "Hello ##name!"
end
end
def main()
helloWorld = HelloWorld.new("Alice")
helloWorld.sayHello
end
main
When trying to delete a directory (+ contents) and after reading the files inside, FileUtils.rm_rf(path) will not delete all the folders, although it does delete all the files and some of the folders.
After some experimentation it seems to be related to a File.open block. (I actually do a regex match inside the block, but I'm just using a puts here to keep things clear)
File.open(file).each do |line|
puts line
end
From what I've read, the above should automatically close the file but when using this, FileUtils fails to complete its task.
However, if I use the following code, FileUtils works as desired.
open_file = File.open(file)
open_file.each do |line|
puts line
end
open_file.close
It's no big deal to use the code in the second example, but I do prefer the cleanliness of the first.
Is there any reason why that first example breaks FileUtils?
P.S. I'm new to both Ruby and Stack Overflow....Hi. My system is Ubuntu 11.04 (64bit), running RVM with Ruby 1.9.2-p180
You should use something like this:
File.open(file) do |f|
f.each{|line| puts line}
end
In your example the block is supplied to the each method and the version of open without a block is executed returning an IO object on which the each method is called.
Here I have two files:
file.rb
def method
puts "This won't be outputted."
end
puts "This will be outputted."
main.rb
require "./file"
When running main.rb it will load all the code inside file.rb so I will get "This will be outputted." on the screen.
Is it possible to load a file without having it to run the code?
Cause I want to load all the methods (in modules and classes too) without having to execute code outside these scopes.
Is it possible to load a file without having it to run the code?
No, everything in a ruby file is executable code, including class and method definitions (you can see this when you try to define a method inside an if-statement for example, which works just fine). So if you wouldn't execute anything in the file, nothing would be defined.
You can however tell ruby that certain code shall only execute if the file is run directly - not if it is required. For this simply put the code in question inside an if __FILE__ == $0 block. So for your example, this would work:
file.rb
def method
puts "This won't be outputted."
end
if __FILE__ == $0
puts "This will not be outputted."
end
main.rb
require "./file"
the if __FILE__ == $0 is nice, but a way more in keeping with ruby's Object Oriented approach is to put all the methods you want access to in a class (as class methods), and then call them from main.rb.
e.g.
file.rb
class MyUtils
def self.method
puts "this won't be outputted"
end
end
and then in main.rb
require "/.file.rb"
and when you want to use your utility methods:
MyUtils.method
I don't think modifying file is good idea - there are could be a lot of files like this one or these files belong to customer and a ton of another reasons.
Ruby is good at metaprogramming so why don't use this feature?
It could be like this.
Create file with fake module and put here the file.
File.open("mfile.rb","w") do |f|
f.write "module FakeModule
"
f.write File.open("file.rb").read
f.write "
end"
end
Then load this file:
require "/.mfile.rb
and accessing to the method:
FakeModule::method