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Changing a certain line in txt file

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  #1  
Old November 9th, 2007, 10:41 AM
csmaster2005 csmaster2005 is offline
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Changing a certain line in txt file
I need to change a certain line in a text file to be something else.
For example, how would I go to the 15th line in a file i've opened and change it to be something like "this is the new 15th line" instead?

Any help is appreciated.
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  #2  
Old November 9th, 2007, 11:08 AM
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You have many choices.
Any of teh following could work:
* IO.each
* IO.each_with_index
* IO.gets
* IO.read
* IO.readlines
* IO.each_line
* IO.pos=
* IO.collect

Try some. Post back with problems.
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If you process text, this might make your life a little easier.
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Old November 9th, 2007, 12:01 PM
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I'm somewhat confused on how to iterate to that line... can you please post code examples?
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Old November 10th, 2007, 06:11 AM
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The File object has an .each method as well as a .readlines method. You can use either one.
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Old November 17th, 2007, 10:38 AM
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As an exercise for the reader (me) I tried the following:

I assumed I can just use readlines and that works fine. Here I loaded the file test.txt and then select the seventh line from f. (offset by zero)

ruby Code:
Original - ruby Code 
    

irb(main):006:0> f=File.open("test.txt").readlines
=> ["this\n", "is\n", "a\n", "test\n", "of\n", "the\n", "emergency\n", "broadcast\n", "system"]
irb(main):007:0> f[6]
=> "emergency\n"


However I tried to use f.each for the file but not sure of it's equivalent as the docs aren't clear.

ruby Code:
Original - ruby Code 
    

irb(main):038:0> f.each {|line|
irb(main):039:1*   if f.lineno ==7:
irb(main):040:2*     puts line
irb(main):041:2>   end
irb(main):042:1> }
=> #<File:test.txt>
irb(main):043:0>


Normally I'd just use readlines, but how would the above f.each method give me the text of the seventh line number?

cheers
sf2k
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  #6  
Old November 17th, 2007, 01:04 PM
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Code:
irb(main):001:0> x = File.open("new_file")
=> #<File:new_file>
irb(main):002:0> x.each { |l| puts l }
Line number 1
Line number 2
Line number 3
Line number 4
Line number 5
Line number 6
=> #<File:new_file>
irb(main):003:0> x.each { |l| puts l }
=> #<File:new_file>
irb(main):004:0> x = File.open("new_file")
=> #<File:new_file>
irb(main):005:0> x.each { |l| puts l }
Line number 1
Line number 2
Line number 3
Line number 4
Line number 5
Line number 6
=> #<File:new_file>
irb(main):006:0>
You have to reload the file again. Or you could do something like:
Code:
irb(main):001:0> x = File.open("new_file")
=> #<File:new_file>
irb(main):002:0> x.each { |l| puts l }
Line number 1
Line number 2
Line number 3
Line number 4
Line number 5
Line number 6
=> #<File:new_file>
irb(main):003:0> x.rewind
=> 0
irb(main):004:0> x.each { |l| puts l }
Line number 1
Line number 2
Line number 3
Line number 4
Line number 5
Line number 6
=> #<File:new_file>
irb(main):005:0>
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