From: Peter Vanderhaden <bostonantifan@...>
Date: 2007-11-23T21:40:19+09:00
Subject: Problem getting user input

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
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