You have single quotes instead of double quotes around the string you want to print
.
class Example
def print_this_var(print_thing)
print 'this is the var: #{print_thing}'
end
end
foo = Example.new
foo.print_this_var("example_text")
#=> this is the var: #{print_thing}
Changing the method definition to
print "this is the var: #{print_thing}"
yields
#=> this is the var: example_text
String interpolation doesn't work with single quotes.