Ruby: check if object is nil

Question

  def parse( line )
    _, remote_addr, status, request, size, referrer, http_user_agent, http_x_forwarded_for = /^([^\s]+) - (\d+) \"(.+)\" (\d+) \"(.*)\" \"([^\"]*)\" \"(.*)\"/.match(line).to_a

    print line
    print request
    if request && request != nil
      _, referrer_host, referrer_url = /^http[s]?:\/\/([^\/]+)(\/.*)/.match(referrer).to_a if referrer
      method, full_url, _ = request.split(' ')

in parse: private method 'split' called for nil:NilClass (NoMethodError)

So as i understand it's calling split not on a string, but on nil. This part is parsing web server log. But I can't understand why it's getting nil. As I understand it's null.

Some of the subpatterns in regex failed? So it's the webserver's fault, which sometimes generates wrong logging strings?

By the way how do I write to file in ruby? I can't read properly in this cmd window under windows.

"As I understand it's null." There is no such thing as null in Ruby. Just nil. — Mark Szymanski
– Mark Szymanski, Commented May 26, 2011 at 18:59
Why what is getting nil? The function is not listed to the end, and you define several variables... — Amadan
– Amadan, Commented May 26, 2011 at 19:00
Mark i know. Amadan it's not my script mate. :) As i understand regex is throwing subpattern matches into listed variables. Like list function in php and when subpattern fails it just assign nil object to it right? — Somebody
– Somebody, Commented May 26, 2011 at 19:01
Actually, wait, it does not make any sense. Are you sure you pasted correctly? If request is nil as your error says, it could not have passed the if request guard. (BTW: if request && request != nil is redundant - if request != nil will always be true if request, which makes the latter sufficient). — Amadan
– Amadan, Commented May 26, 2011 at 19:10
Indeed. I don't know Ruby, so the statement should be different. Maybe !== instead of != should be used? I'll try that out. — Somebody
– Somebody, Commented May 26, 2011 at 19:13

Chris Bunch · Accepted Answer · 2011-05-26 19:14:35Z

41

You seem to have a few questions here, so I'll take a stab at what seems to be the main one:

If you want to see if something is nil, just use .nil? - so in your example, you can just say request.nil?, which returns true if it is nil and false otherwise.

answered May 26, 2011 at 19:14

Chris Bunch

90.5k37 gold badges130 silver badges128 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Somebody Over a year ago

I'll catch request that fails and see why pattern is failing. Questiong is still opened. Why it passes statement? :)

user513951 · Accepted Answer · 2021-10-19 16:11:47Z

12

Ruby 2.3.0 added a safe navigation operator (&.) that checks for nil before calling a method.

request&.split(' ')

This is functionally* equivalent to

!request.nil? && request.split(' ')

*(They are slightly different. When request is nil, the top expression evaluates to nil, while the bottom expression evaluates to false.)

edited Oct 19, 2021 at 16:11

answered Apr 14, 2016 at 18:51

user513951

14k8 gold badges71 silver badges91 bronze badges

Comments

Amadan · Accepted Answer · 2011-05-26 19:04:03Z

3

To write to a file:

File.open("file.txt", "w") do |file|
  file.puts "whatever"
end

As I write in a comment above - you didn't say what is nil. Also, check whether referrer contains what you think it contains. EDIT I see it's request that is nil. Obviously, regexp trouble.

Use rubular.com to easily test your regexp. Copy a line from your input file into "Your test string", and your regexp into "Your regular expression", and tweak until you get a highlight in "Match result".

Also, what are "wrong logging strings"? If we're talking Apache, log format is configurable.

answered May 26, 2011 at 19:04

Amadan

200k23 gold badges252 silver badges321 bronze badges

14 Comments

Somebody Over a year ago

Mate... :) Why it's passing through this? if request && request != nil

Amadan Over a year ago

Yeah, I know, I just commented on that. That should be impossible.

Somebody Over a year ago

How to check in Ruby that some variable, in our case it's request is not an instance of nil?

Amadan Over a year ago

if !request.nil? - but if request suffices (in Ruby, nil and false are the only values that will fail an if, and you can't get false here to confuse the issue).

Amadan Over a year ago

No, the current directory. If you are located in /path/to/my/prompt but start your script with /path/to/my/script.rb, then it will write the file as /path/to/my/prompt/file.txt. It will only write in the directory of the ruby script if you're there as well.

|

Collectives™ on Stack Overflow

Ruby: check if object is nil

3 Answers 3

1 Comment

Comments

14 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

14 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related