Asp Forum - Simple Reading, Deleting and Writing to Files

Skeets

8/5/2006 4:25:00 AM

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 address@url.com
#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...

4 Answers

James Britt

8/5/2006 5:01:00 AM

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.

>
> can anyone point me to a tutorial or lend a hand?
>

Look at

http://www.ru.../core/class...

and

http://www.ru.../core/classes...

Note that the File class inherits from IO, so behavior of interest may
be defined in either place.

--
James Britt

http://www.ru... - Ruby Help & Documentation
http://www.artima.c... - The Journal By & For Rubyists
http://www.rub... - The Ruby Store for Ruby Stuff
http://www.jame... - Playing with Better Toys
http://www.30seco... - Building Better Tools

Skeets

8/5/2006 6:15:00 AM

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.

William James

8/5/2006 7:02:00 AM

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.

Robert Klemme

8/5/2006 8:49:00 AM

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

comp.lang.ruby

Simple Reading, Deleting and Writing to Files

Skeets

James Britt

Skeets

William James

Robert Klemme

x Login to ForumsZone