From: Wesley J Landaker <wjl@...>
Date: 2003-08-01T13:56:51+09:00
Subject: Re: A bundle of newbie queries

On Thursday 31 July 2003 10:26 pm, Gawnsoft wrote:

> 1) After the file has been opened and I've iterated through it once,
> I can't successfully iterate through the opened file for something
> else. e.g.
>
>    dictionary2 = Hash.new(0)

aFile.rewind
(see http://www.rubycentral.com/book/ref_c_io.html#IO.rewind)

>    aFile.each_line { | eachLine | dictionary2[ /[0-9.]+/ ] =
> dictionary2[ /[0-9.]+/ ] + 1 if eachLine.include?("anotherfile") }

> 2) I then tried to get the no-longer usable file garbage-collected by
> IRB-ing
>
>    aFile = nil
>
> but even after evaluating this statement, another windows app still
> fails to be able to over-write copyOfGeneral.txt
>
> What should I do to get Ruby to 'free up' the file?

aFile.close

If you don't close a file that you opened it will [probably(?)] get 
closed when it gets garbage collected. Note that you only need to close 
a file if you do this:

f = File.open(...)
do stuff with f
f.close

If you do it this way, it will get closed for you automatically:

File.open(...) { |f|
  do stuff with f
}


> -----------
> 3) I tried to cut it down from 4 lines of code to 3 lines of code by
> using:
>    (File.open("d:/Data/Logs/Savant/copyOfGeneral.txt")).each_line {
>
> |line| blah... }
>
> I'm sure I've seen snippets of code in the newsgroup that call
> methods from the result of called methods, although the real reason I
> tried it is because I'm currently learning Smalltalk where
>
>    ( File open: "name of aFile" ) each_line: [ blah... ]     #
> pseudocode only this, in all probability, btw
>
> works as the parenthesised expression is evaluated first and returns
> aFile, which is then sent the eac_line message

This should work just fine; what kind of error are you getting?

File.open(...).each_line { |line|
  # use line here
}

> What are the rules as to when   object.method.method    is a valid
> Ruby construct?   Is it ever a valid Ruby construct?

It's practically always valid, unless you are doing something 
syntactically weird or ambiguous... so you can do stuff like this:

line = "Apples are nice, but cheese whiz is better."
line.chomp.gsub(/whiz/,'sauce').sub(",") { '' }.split.to_a.join("!!! ")
#=> "Apples!!! are!!! nice!!! but!!! cheese!!! sauce!!! is!!! better."

> ------------
> 4) I'd like to c'n'p a multi-line method into IRB all at once.  Can
> I? And if so, how?
>
> def countDownloads (aFile, aString)
>
>   anIpNum = Regexp.new('[0-9.]+')
>
>   aDictionary = Hash.new(0)
>
>   aFile.each_line { | line | aDictionary[line.slice(anIpNum)] =
> aDictionary[line.slice(anIpNum)] + 1 if line.include?(aString) }
>
>   puts aDictionary.size
>
> end

You should just be able to copy and paste it, it works fine here. =)

> 5) I'd like to save this method as a .rb file, and invoke it from
> IRB. How do I?

If the code is in "file.rb", then in irb:

irb> load "file.rb"

> 6) I'd like to change the current Windows directory from within IRB.
> How do I?
>
> Using irb_context, I saw there was an irb_path set (to be '(irb)' so
> I tried: conf.irb_path="d:/data/grlcode"  which returned:
> NameError: undefined local variable or method `conf' for
> #<Object:0x463b638>

Dir.chdir("d:/data/grlcode") should work just fine. =)

>
> Cheers,
>    Euan

Hope that helped! You'll probably get other [better?] answers from some 
other folks here on the list as well.

-- 
Wesley J. Landaker - wjl@icecavern.net
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