Ruby comes with a lot of constants that hold various information. Here are some common constants :
ARGF is a stream built when passing in a list of files to be processed using arguments to an application. As a file is processed by
ARGF it is removed from the ARGV array so that it it not re-processed.
ARGF is a stream designed for use in scripts that process files given as command-line arguments or passed in via STDIN.
The arguments passed to your script are stored in the ARGV Array, one argument per element. ARGF assumes that any arguments that aren't filenames have been removed from ARGV. For example:
$ ruby argf.rb --verbose file1 file2 ARGV #=> ["--verbose", "file1", "file2"] option = ARGV.shift #=> "--verbose" ARGV #=> ["file1", "file2"]
You can now use ARGF to work with a concatenation of each of these named files. For instance, ARGF.read will return the contents of file1 followed by the contents of file2.
After a file in ARGV has been read ARGF removes it from the Array. Thus, after all files have been read ARGV will be empty.
You can manipulate ARGV yourself to control what ARGF operates on. If you remove a file from ARGV, it is ignored by ARGF; if you add files to ARGV, they are treated as if they were named on the command line. For example:
ARGV.replace ["file1"] ARGF.readlines # Returns the contents of file1 as an Array ARGV #=>  ARGV.replace ["file2", "file3"] ARGF.read # Returns the contents of file2 and file3
It is an alias of $*. Holds command line arguments
#!/usr/bin/env ruby count = ARGV.count puts ARGV if count > 0
Read portions of the code marked with END and ends at the end of the file.
Read environment variables.
irb(main):012:0> ENV["HOME"] => "/Users/joseph"
Constants hold information about Ruby. Here are some constants :
Make an object read-only.
irb(main):014:0> results = [10, 120, 57] => [10, 120, 57] irb(main):015:0> results.freeze => [10, 120, 57] irb(main):016:0> results.frozen? => true irb(main):017:0> results.pop RuntimeError: can't modify frozen Array
We can check object metadata using methods such as
instance_of? as follows :
>> class Person >> end => nil >> p = Person.new => #<Person:0x007fad4d0032f8> >> p1 = Person.new => #<Person:0x007fad4c20ed78> >> p.instance_of? Person
We can use the
is_a? method to check if an object is an instance of the type as follows :
>> class Person >> end => nil >> p = Person.new => #<Person:0x007fad4d0032f8> >> p.is_a? Person => true