From: Morton Goldberg <m_goldberg@...>
Date: 2007-11-24T02:09:00+09:00
Subject: Re: Problem getting user input

On Nov 23, 2007, at 7:40 AM, Peter Vanderhaden wrote:

> I wrote a script that gets user input like this:
>
>    $stdout.print "Do you want to change something else? (y/n): "
>    $changeSE = gets.chomp
>    if $changeSE =~ /^y/
>      changeSomethingElse
>    end
>
> After the prompt is printed, the script waits for the user to enter  
> yes
> or no via stdinput.  The script was written in a procedural format as
> opposed to OO.  (I did that only because I'm in the process of  
> learning
> OO, and needed the script asap.)  I decided to rewrite the script  
> using
> OO.  Unfortunately, this part of the script doesn't work anymore.  The
> prompt prints, then the script keeps going on its merry way.  I've
> included the source for the script below.  Can anyone (or everyone)  
> see
> what I'm not doing correctly?  If so, I'd appreciate it if you could
> explain how to correct the problem.  I'd be extremely grateful for any
> and all comments and assistance.
> PV
>
>  1 #!/usr/bin/ruby
>  2 #
>  3 # fix1.rb - Fix common unitization file errors.
>  4 #           1. Remove header line.
>  5 #           2. Populate vendor label field with "NULL".
>  6 #           3. Change .TIF extension to lower case.
>  7 #
>  8 class Record
>  9
> 10     # Constructor.
> 11     def initialize (record_string)
> 12         @record = record_string
> 13     end
> 14
> 15     # Populates the volume label.
> 16 # regex: Start at the beginning of the line, match
> 17 # all non-comma characters, followed by 2 commas.
> 18     def fix_volume_label
> 19 #      @record.sub!(/\d,,/,',NULL,')
> 20        @record.sub!(/^([^,]*),,/, '\1,NULL,')
> 21     end
> 22
> 23     # Change file extension to lowercase.
> 24     def fix_extension_case
>  25        @record.sub!('.TIF','.tif')
>  26     end
>  27
>  28     # Allow user to do a generic fix.
>  29     def changeSomethingElse
>  30        @record.sub!(before,after)
>  31     end
>  32
>  33     # Returns fixed record as a string
>  34     def to_str
>  35        @record
>  36     end
>  37
>  38 end
>  39
>  40 # Main thread of execution.
>  41 class FixOpt
>  42
>  43   def initialize
>  44
>  45       @ARGV = $*                # list of arguments passed to the
> script
>  46       @header_regex = /BegBates,Volume,Path/
> 47
> 48       @in_file = nil
> 49 #     @out_file = nil
> 50       unless arguments_valid? @ARGV
> 51           usage
> 52           exit -1
> 53       end
> 54
> 55 # Does user want to change something else?
> 56  def checkChange
> 57      puts "Do you want to change something else (y/N): "
> 58      changeIt = gets
> 59      if changeIt =~ /^[yY]/
> 60         puts "Enter string to change: "
> 61         before = gets.chomp
> 62         puts "Enter new string:       "
> 63         after = gets.chomp
> 64         puts "Global change? (N/y):   "
> 65         global = gets.chomp
> 66      end
> 67  end # End checkChange method.
> 68
> 69         begin
> 70             @in_file = File.new @ARGV[0], "r"
> 71         rescue IOError
> 72             @in_file.close
> 73             puts "Error opening input file, terminating"
> 74             exit -1
> 75         end
> 76
> 77   end # End initialize method.
> 78
> 79 # Runs the program - the [C]ontroller portion of the MVC pattern.
> 80     def run
> 81         begin
> 82            checkChange
> 83             @in_file.each do |record_line|
> 84                 next if record_line =~ @header_regex
> 85                 record = Record.new(record_line)
> 86                 record.fix_volume_label
> 87                 record.fix_extension_case
> 88                if changeIt =~ /^[yY]/
> 89                   record.changeSomethingElse
> 90                end
>  91                 puts record.to_str
>  92             end
>  93         rescue IOError
>  94             @in_file.close
>  95             puts "Error reading from input file, terminating"
>  96             exit -1
>  97         end
>  98         @in_file.close
>  99         exit 0 # success!
> 100     end
> 101
> 102     # these methods are marked :private becuase they are never  
> to be
> called
> 103     # from anywhere outside of the class itself.
> 104     :private
> 105
> 106     # Validates command line arguments.
> 107     def arguments_valid? (argv)
> 108 # readable assumes the file exists, but doesn't check for it.
> 109 #        File.stat(ARGV[0]).readable?
> 110 # Returns true if the named file exists and is a regular file.
> 111         File.file?(ARGV[0])
> 112     end
> 113
> 114     # Prints the usage message
> 115     def usage
> 116         puts
> 117         puts "Invalid filename entered: #{ARGV[0]}"
> 118         puts "Syntax: fix1.rb <filename>"
> 119         puts
> 120     end
> 121
> 122 end
> 123 fix_opt = FixOpt.new
> 124 fix_opt.run
>
> If I use gets, the script just prints the prompt and seems to end.
> If I use gets.chomp I get the following error:
> $ ruby d:/scripts/ruby/fix1.rb 99999.opt
> Do you want to change something else (y/N):
> d:/scripts/ruby/fix1.rb:58:in `checkChange': private method `chomp'
> called for nil:NilClass (NoMethodEr
> ror)
>         from d:/scripts/ruby/fix1.rb:82:in `run'
>         from d:/scripts/ruby/fix1.rb:124

I can not reproduce your problem. When I run

<code>
class Foo
    def checkChange
       puts "Do you want to change something else (y/N): "
       changeIt = gets.chomp
       if changeIt =~ /^[yY]/
          puts "Enter string to change: "
          before = gets.chomp
          puts "Enter new string:       "
          after = gets.chomp
          puts "Global change? (N/y):   "
          global = gets.chomp
       end
       p [changeIt, before, after, global]
    end
end
Foo.new.checkChange
</code>

I see the following

<result>
Do you want to change something else (y/N):
Enter string to change:
Enter new string:
Global change? (N/y):
["y", "foo", "bar", "n"]
</result>

I will note the variables changeIt, before, after, and global are  
local variables and will not available outside of the checkChange  
method. That may be part of your problem.

Regards, Morton