Why set hash with 'eval' doesn't work?

Ruby
1

=========================

  1. cat list
    =========================
    lic_servers = {
    ‘10071@server1’ => 10,
    ‘10072@server2’ => 10
    }
    =========================
  2. cat test.rb
    =========================
    #!/usr/bin/env ruby

csh_file = ‘list’
sign = cat #{csh_file}
a = eval(sign)
puts a

puts lic_servers

=========================
3. run test.rb

{“10071@server1”=>10, “10072@server2”=>10}
test.rb:8:in <main>': undefined local variable or methodlic_servers’
for main:Object (NameError)

Why it report ‘lic_servers’ undefined? I hope lic_servers set by ‘eval’,
but seems doesn’t work, why?

  • The object set lic_servers in file ‘list’ is for the servers list
    always change, I want split it from main ruby script.
2

See

Eval creates the variable in his own scope. If you want is to be
available you should use an instance variable

@lic_servers = {…}

and in test.rb

puts @lic_servers

Lars

3

Another way is to define the local var before the eval so that it will
be accessible after it.

=========================
2. cat test.rb

#!/usr/bin/env ruby

lic_servers = Hash.new # <-- Define it before
csh_file = ‘list’
sign = cat #{csh_file}
a = eval(sign)
puts a

puts lic_servers

=====

Another example.

10.times do |x|
my_local = x
end

if defined? my_local
puts “my_local = #{my_local}”
else
puts “my_local is not defined”
end

Second round with local var being defined outside the block

my_local = 0

10.times do |x|
my_local = x
end

if defined? my_local
puts “my_local = #{my_local}”
else
puts “my_local is not defined”
end

This outputs

my_local is not defined
my_local = 9

Abinoam Jr.

4

Lars Vonk wrote in post #1132612:

See
ruby - Variable assignment using eval - Stack Overflow

Eval creates the variable in his own scope. If you want is to be
available you should use an instance variable

@lic_servers = {…}

and in test.rb

puts @lic_servers

Lars

Eval creates the variable in his own scope
Understand now, many thanks.

If you want is to be
available you should use an instance variable

@lic_servers = {…}

May I ask one more question? As I know, instance variable should belongs
to specific class, so here @lic_servers belongs to which class, Main
class?

5

Dear Alex,

Thank you so much for your guide and help, I understand now.

6

On Thu, Jan 9, 2014 at 5:37 PM, Previn L. [email protected] wrote:

May I ask one more question? As I know, instance variable should belongs
to specific class, so here @lic_servers belongs to which class, Main
class?

This is a great question. Actually, an instance variable belongs to an
instance, not a class. You can tell which instance by looking at the
self variable. At the top level self points to a magic object called
main (not Main) so that’s where @lic_servers lives.

Type “self” and “self.class” at irb to see for yourself.

If it’s still unclear, maybe my slides at
Objects - Code Like This will
clarify.