Ruby eval在irb和文件中的行为不同

问题描述

此代码在irb中有效：

This code works in irb:

irb(main):037:0> eval <<-EOS
irb(main):038:0" #{attribute} = "host"
irb(main):039:0" puts machine
irb(main):040:0" EOS
host
=> nil
irb(main):041:0> puts machine
host
=> nil
irb(main):042:0> puts attribute
machine
=> nil
irb(main):043:0>

但是，当我尝试执行与ruby脚本相同的代码时，出现以下错误：

however when I try to execute the same code as a ruby script I get the following error:

../autosys/convert_jil_to_zapp.rb:40: undefined local variable or method `machine' for main:Object (NameError)
        from ../autosys/convert_jil_to_zapp.rb:29:in `each_line'
        from ../autosys/convert_jil_to_zapp.rb:29
        from ../autosys/convert_jil_to_zapp.rb:27:in `each'
        from ../autosys/convert_jil_to_zapp.rb:27
pi929c1n10 /ms/user/h/hirscst/ruby/autosys 77$ gvim try.rb
pi929c1n10 /ms/user/h/hirscst/ruby/autosys 78$ chmod +x try.rb
pi929c1n10 /ms/user/h/hirscst/ruby/autosys 79$ ./try.rb
host
./try.rb:8: undefined local variable or method `machine' for main:Object (NameError)

有人可以解释原因吗？

推荐答案

这是因为 eval 时，尚未定义> machine 变量。一个更简洁的示例：

It's because the machine variable was not already defined when eval was run. A more concise example:

eval 'x = 3'
puts x # throws an exception when run as a script
=> 3

在IRB中作为脚本工作

Works in IRB and as a script

x = 1
eval 'x = 3'
puts x
=> 3

致：

不同之处在于，在IRB中，所有内容都在评估中，因此它们都在同一范围内。也就是说，您实际上是在IRB中执行此操作：

The difference is that in IRB everything is being eval'd, so it's all in the same scope. That is, you're essentially doing this in IRB:

eval 'x = 3'
eval 'puts x'

在IRB和脚本中都可以工作。

Which works both in IRB and as a script.

这篇关于Ruby eval在irb和文件中的行为不同的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！