# Re: Newbie syntax questions

**URL:** <https://www.ruby-forum.com/t/re-newbie-syntax-questions/68314>\
**Category:** Ruby\
**Created:** [September 11, 2006, 6:08pm UTC](https://www.ruby-forum.com/t/re-newbie-syntax-questions/68314 "2006-09-11T18:08:38Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![phrogz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/2acd7d/32.png) [@phrogz](https://www.ruby-forum.com/u/phrogz)\
**Post date:** [September 11, 2006, 6:08pm UTC](https://www.ruby-forum.com/t/re-newbie-syntax-questions/68314/1 "2006-09-11T18:08:38Z")

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> 1. Why is there an equals sign in the code “def  
> self.run=(flag)” and what  
> does it do?

Methods can have an equals sign at the end of their name. Ruby calls  
these methods when you write something that LOOKS like you’re assigning  
to a property:

class Foo  
def bar=( new\_value )  
puts “I’m going to set a new value of #{new\_value}!”  
@some\_var = new\_value  
end  
end

f = Foo.new  
f.bar = “Hello World”  
#=\> I’m going to set a new value of Hello World!

> 1. Why is there an equals sign in the code “@run ||= false”  
> and what does  
> it do?

a ||= b  
is shorthand for  
a = a || b  
just like a += b is shorthand for a = a + b

Because the || operator does not return a boolean value, but rather the  
first operand that isn’t a non-truth value, the above code is equivalent  
to:

@run = if @run  
@run  
else  
false  
end

In practical application, what it’s saying is:  
“If the @run variable is nil or false, set the value to false”.  
or precisely:  
“If the @run variable is nil (probably because it hasn’t been assigned  
to a value yet), please set it to false.”

> 1. What does “$0 != “-e” && $0” mean and do?

$0 is a global variable that holds the name of the currently-running  
script.  
If you run “ruby foo.rb” then $0 will be the string “foo.rb”.  
If you run ruby with the -e option, it will evaluate the string you  
supply as ruby code. For example, “ruby -e ‘p 1+1’” will print 2.

When run like this, $0 is set to “-e”, because there is no file name.

SO, the above code is saying “If $0 isn’t -e, then the name of the  
currently-running file.” Like ||, the && operator doesn’t actually  
return true or false, it returns the value of the left side if the left  
side is a non-truth value (false or nil), or the value of the right  
side.

The $0!="-e"&&$0 bit is a terse (obfuscated?) way of saying “if the  
script being run is off of the command line, use a value of false;  
otherwise, use the value of the currently-running file name”