William James wrote:
> Skeets wrote:
>> James Britt wrote:
>>> 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)}
>>>
>>>> 2. 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.
>> 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.
> 
> 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.

Here's another alternative: use "ruby -i.bak" to change the file in 
place, like

$ cat ip.txt
#ip 127.0.0.1
#email address / url.com
#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 address / url.com
#duration 600

robert@fussel /cygdrive/c/Temp
$ cat ip.txt.bak
#ip 127.0.0.1
#email address / url.com
#duration 600

robert@fussel /cygdrive/c/Temp
$

Kind regards

	robert