1) at_exit { code to be executed}
This method starts the execution of the code when the program exits.
For Example:

puts "Begining of execution"
at_exit do
  puts "Inside at_exit"
end
puts "End of execution"

Output:

Begining of execution
End of execution
Inside at_exit

2) autoload(classname, file_path)
It loads the class from the given filename. Here classname can be a string or symbol. Autoload works like require but the difference is that the file is only required when the constant is accessed, which can speed up your program.

Let's say you have a file called example.rb containing the following code:

puts "Welcome user!"

class MyClass
end

Now open irb and use require to load the example.rb

irb(main):001:0> require 'example'
Welcome user!
=> true

Now again open irb and use autoload:

irb(main):001:0> autoload :MyClass, 'example'
=> nil
irb> MyClass
Welcome user!
=> MyClass

3) eval(str)
To evaluate and compile a string you can do it by using eval. Its return value is the value of the last expression of the program.
For example:

p eval("1 + 1")   # 2

we can also refer to a variable in its scope from inside of a string to `eval`.

first_var = 5
@second_var = 6
p eval("first_var + @second_var")   # 11

4) chop()
Chop method returns the value of string after removing its last character. If the string ends with rn, both characters are removed.

For example:

"Apple\r\n".chop   #=> "Apple"
"Apple\n\r".chop   #=> "Apple\n"
"Apple\n".chop     #=> "Apple"

5) proc {| x|...}
The block is been converted into Pro object by Proc converts. Proc objects are blocks of code that have been bound to a set of local variables.
For example:

proc_1 = Proc.new { |x| puts x*2 }
[1,2,3].each(&proc_1)

proc_2 = Proc.new { puts "Hello World" }
proc_2.call

6) sleep( 10 )
Suspends program execution for seconds specified. If the second isn't specified, the program is suspended forever.