Using same ruby block is now throwing errors

Question

Consider this block of code:

f = File.new('test')
f.each_line { |line|
  if line =~ /@b/ then
    x = line
  end
}
y = x[/<(.*)>/,1]

This is f:

@a <1,2,3>
@b <'whatever'>
@c <['x','y','z']
@d <1.1>

and Originally, this block of code was working, returning y as 'whatever', but is now throwing this error:

Traceback (most recent call last):
        4: from C:/Ruby26-x64/bin/irb.cmd:31:in `<main>'
        3: from C:/Ruby26-x64/bin/irb.cmd:31:in `load'
        2: from C:/Ruby26-x64/lib/ruby/gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `<top (required)>'
        1: from (irb):10
NameError (undefined local variable or method `x' for main:Object)

Any suggestions?

P.S.

This is being run directly through irb

What statement is on line 10 ('10' being from your error message)? You need to pay careful attention to error messages; often the pinpoint the problem. — Cary Swoveland
– Cary Swoveland, Commented Dec 19, 2019 at 7:25
You are aware that if multiple lines match @b then x will only represent the last one correct? — engineersmnky
– engineersmnky, Commented Dec 19, 2019 at 14:02
If you want all matches you could do something like: lines = File.foreach('test').grep(/@b/) — 3limin4t0r
– 3limin4t0r, Commented Dec 19, 2019 at 17:05

Gavin Miller · Accepted Answer · 2019-12-19 04:40:48Z

4

x is being defined in the local context of the block, and once the context of the block is left it is no longer defined. So variable x needs to be defined outside the context of the block:

x = nil
f = File.new('test')
f.each_line { |line|
  if line =~ /@b/ then
    x = line
  end
}
y = x[/<(.*)>/,1]

answered Dec 19, 2019 at 4:40

Gavin Miller

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1 Comment

Cary Swoveland Over a year ago

You might show how you are using the initial value of x in the event that no line matches /@b/: y = x.nil? ? nil : x[/<(.*)>/,1].

ChuckCottrill · Accepted Answer · 2019-12-19 04:43:12Z

2

Scope. Define x, then run in irb, and note that it works…

x = 'not in scope'
f = File.new('test')
f.each_line { |line|
  if line =~ /@b/ then
    x = line
  end
}
y = x[/<(.*)>/,1]

answered Dec 19, 2019 at 4:43

ChuckCottrill

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