How to write in the middle of a file

ruby-talk
1

Greetings all. For some reason the answer to this stumps me.
Say I have an existing file, 1K long, and I want to write something
right in the middle of it, without changing the file size.
I would have thought that
a = File.open 'file', 'a+'
a.seek 500
a.write 'abc'
a.close

would work but doesn't seem to. Thoughts?
-R

···

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2

Greetings all. For some reason the answer to this stumps me.
Say I have an existing file, 1K long, and I want to write something
right in the middle of it, without changing the file size.

meaning you want to OVERWRITE something in the middle, yes?

I would have thought that
a = File.open 'file', 'a+'
a.seek 500
a.write 'abc'
a.close

would work but doesn't seem to. Thoughts?
-R

Try a mode of 'r+'. The 'a' part says you want all the writes to go the the end-of-file (whatever that happens to be at the time).

File.open 'file', 'w' do |f| f.write 'x'*1024 end

a = File.open 'file', 'r+'
a.seek 500
a.write 'abc'
a.close

all = File.read('file')

puts all.size

1024
=> nil

puts all.index('abc')

500
=> nil

You can puts(all) yourself if you want :wink:

-Rob

Rob Biedenharn http://agileconsultingllc.com
Rob@AgileConsultingLLC.com

···

On Jun 25, 2008, at 8:59 PM, Roger Pack wrote:

3

Try a mode of 'r+'. The 'a' part says you want all the writes to go
the the end-of-file (whatever that happens to be at the time).

Works like a charm. You rock!
-R

···

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