# Simple Reading, Deleting and Writing to Files **URL:** \ **Category:** Ruby\ **Created:** [August 5, 2006, 6:26am UTC](https://www.ruby-forum.com/t/simple-reading-deleting-and-writing-to-files/101476 "2006-08-05T06:26:43Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Skeets](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/8e8cbc/32.png) [@Skeets](https://www.ruby-forum.com/u/Skeets)\ **Post date:** [August 5, 2006, 6:26am UTC](https://www.ruby-forum.com/t/simple-reading-deleting-and-writing-to-files/101476/1 "2006-08-05T06:26:43Z")
i have done some research, but can’t see anything that explains simple file writing. eventually, i may end using rexml, but for now i just want to use a simple text file. ip.txt contains three lines of text. they are as follows: #ip 127.0.0.1 #email removed\_email\_address@domain.invalid #duration 600 thanks to help i received on this forum, i know how to open the file. i also figured out how to grep a line of text and then manipulate the line so i get only the data of interest. what i don’t know how to do is to… 1. write this data to a newly created file (case: file doesn’t exist) 2. overwrite the data (case: file exists but data needs to be updated). eg, let’s say my ip changed to 127.0.0.2. i want to delete “#ip 127.0.0.1” and replace it with “#ip 127.0.0.2”. i i’d also consider if deleting just 127.0.0.1 and replacing it with 127.0.0.2 if it makes more sense. can anyone point me to a tutorial or lend a hand? tia… ---
**Author:** ![Skeets](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/8e8cbc/32.png) [@Skeets](https://www.ruby-forum.com/u/Skeets)\ **Post date:** [August 5, 2006, 7:02am UTC](https://www.ruby-forum.com/t/simple-reading-deleting-and-writing-to-files/101476/2 "2006-08-05T07:02:46Z")
Skeets wrote: > what i don’t know how to do is to… > > 1. write this data to a newly created file (case: file doesn’t exist) File.open( some\_file\_name, ‘w’){|f| f.puts(the\_data)} > 1. overwrite the data (case: file exists but data needs to be updated). > You can use the same code. It will overwrite the current file with the > new data. > eg, let’s say my ip changed to 127.0.0.2. i want to delete “#ip > 127.0.0.1” and replace it with “#ip 127.0.0.2”. i i’d also consider if > deleting just 127.0.0.1 and replacing it with 127.0.0.2 if it makes > more sense. Just overwrite the old file with the new, complete, data. > can anyone point me to a tutorial or lend a hand? Look at [http://www.ruby-doc.org/core/classes/IO.html](http://www.ruby-doc.org/core/classes/IO.html) and [class File - RDoc Documentation](http://www.ruby-doc.org/core/classes/File.html) Note that the File class inherits from IO, so behavior of interest may be defined in either place. – James B. [http://www.ruby-doc.org](http://www.ruby-doc.org) - Ruby Help & Documentation [Ruby Code & Style](http://www.artima.com/rubycs/) - The Journal By & For Rubyists [http://www.rubystuff.com](http://www.rubystuff.com) - The Ruby Store for Ruby Stuff [http://www.jamesbritt.com](http://www.jamesbritt.com) - Playing with Better Toys [http://www.30secondrule.com](http://www.30secondrule.com) - Building Better Tools ---
**Author:** ![Skeets](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/8e8cbc/32.png) [@Skeets](https://www.ruby-forum.com/u/Skeets)\ **Post date:** [August 5, 2006, 8:20am UTC](https://www.ruby-forum.com/t/simple-reading-deleting-and-writing-to-files/101476/3 "2006-08-05T08:20:49Z")
James B. wrote: > You can use the same code. It will overwrite the current file with the > new data. > > > eg, let’s say my ip changed to 127.0.0.2. i want to delete “#ip > > 127.0.0.1” and replace it with “#ip 127.0.0.2”. i i’d also consider if > > deleting just 127.0.0.1 and replacing it with 127.0.0.2 if it makes > > more sense. > > Just overwrite the old file with the new, complete, data. thanks for the tip. at first glance, though, i’m thinking i want to delete only the line(s) that change. eg, if the i line changes, i don’t want to read in the whole file, i’d prefer to just overwrite the #ip line. is this doable? if so, is it too much trouble for a short file like this one? i perused the linked references, but didn’t find a way to delete a specific line and replace it. thanks again. ---
**Author:** ![Skeets](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/8e8cbc/32.png) [@Skeets](https://www.ruby-forum.com/u/Skeets)\ **Post date:** [August 5, 2006, 9:05am UTC](https://www.ruby-forum.com/t/simple-reading-deleting-and-writing-to-files/101476/4 "2006-08-05T09:05:52Z")
Skeets wrote: > > > 1. overwrite the data (case: file exists but data needs to be updated). > > thanks again. Load the whole file that you want to change into an array. Each element of the array is a line of the file. Change a line. Write the lines back to the file. ---
**Author:** ![Skeets](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/8e8cbc/32.png) [@Skeets](https://www.ruby-forum.com/u/Skeets)\ **Post date:** [August 5, 2006, 10:50am UTC](https://www.ruby-forum.com/t/simple-reading-deleting-and-writing-to-files/101476/5 "2006-08-05T10:50:55Z")
William J. wrote: > > > You can use the same code. It will overwrite the current file with the > > > #ip line. > > > Each element of the array is a line of the file. > > > Change a line. > > > Write the lines back to the file. Here’s another alternative: use “ruby -i.bak” to change the file in place, like $ cat ip.txt #ip 127.0.0.1 #email removed\_email\_address@domain.invalid #duration 600 robert@fussel /cygdrive/c/Temp $ ruby -i.bak -p -e ‘$\_.gsub!(/^#ip (\d+(?:.\d+){3})/, “#ip 127.0.0.2”)’ ip.txt robert@fussel /cygdrive/c/Temp $ cat ip.txt #ip 127.0.0.2 #email removed\_email\_address@domain.invalid #duration 600 robert@fussel /cygdrive/c/Temp $ cat ip.txt.bak #ip 127.0.0.1 #email removed\_email\_address@domain.invalid #duration 600 robert@fussel /cygdrive/c/Temp $ Kind regards ``` robert ```