# Read and modify logs

**URL:** <https://www.ruby-forum.com/t/read-and-modify-logs/164378>\
**Category:** Ruby\
**Created:** [March 31, 2009, 5:41pm UTC](https://www.ruby-forum.com/t/read-and-modify-logs/164378 "2009-03-31T17:41:16Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![mifi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7993a0/32.png) [@mifi](https://www.ruby-forum.com/u/mifi)\
**Post date:** [March 31, 2009, 5:41pm UTC](https://www.ruby-forum.com/t/read-and-modify-logs/164378/1 "2009-03-31T17:41:16Z")

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I’m trying to read the entries in a logfile so I can enter its contents  
in a database, the lines are results I want to record, but in order to  
be sure that I don’t have duplicates I’d like to be able to remove  
entries that I have read. Is there an easy way to do this in Ruby so I  
can remove read lines from a file that is open once they’ve been  
captured?

I’m not as worried about the conn\_to\_db.print line, that is something I  
have working ok, so if it looks funny please ignore it.

What I have so far, and its untested as of yet as I am trying to get the  
form right, until I am sure its working .

Example:  
while running  
sleep 10

# read file into an array

f = file.open(“mylogfile.log”)  
saved = File.open(“archive.log”, “a”)  
results = f.readlines

# Is there a way to remove everything that’s been read here?

f.close  
results.each\_line do |sending|  
conn\_to\_db.print(“data #{sending}”)  
# Make sure we keep a backup  
saved.puts("#{sending}") s.flush  
end

# Close the archive file

saved.close  
end

Thanks for any help!

---

<div class="post-metadata">

**Author:** ![mifi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7993a0/32.png) [@mifi](https://www.ruby-forum.com/u/mifi)\
**Post date:** [April 2, 2009, 7:00am UTC](https://www.ruby-forum.com/t/read-and-modify-logs/164378/2 "2009-04-02T07:00:37Z")

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There’s at least a couple of ways to remove duplicate lines.

1. results.uniq!
2. results.each { |l| b\<\<l } # b.keys gives you the set of unique lines

Hope that helps,

Jayanth

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<div class="post-metadata">

**Author:** ![mifi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7993a0/32.png) [@mifi](https://www.ruby-forum.com/u/mifi)\
**Post date:** [April 2, 2009, 7:12am UTC](https://www.ruby-forum.com/t/read-and-modify-logs/164378/3 "2009-04-02T07:12:54Z")

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Sorry, I misread your question.

One silly way to achieve what you want is to reopen the file for  
reading.  
That would pretty much erase the file. Not sure if that’s what you  
want…

f.close  
f = File.open(“mylogfile.log”,“w”)  
f.close

Though, I don’t see why you can’t maintain a hash of all the lines  
instead  
of having to remove lines from the log file. Its never a good idea to  
muck  
about with log files.

Jayanth

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<div class="post-metadata">

**Author:** ![mifi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7993a0/32.png) [@mifi](https://www.ruby-forum.com/u/mifi)\
**Post date:** [April 2, 2009, 2:16pm UTC](https://www.ruby-forum.com/t/read-and-modify-logs/164378/4 "2009-04-02T14:16:53Z")

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Srijayanth S. wrote:

> One silly way to achieve what you want is to reopen the file for  
> reading.

I wanted to avoid that as I am using this log file to maintain results  
from other scripts and if the timing goes wrong I might close the file,  
another opens, then I open it again to erase and lose the latest entry.  
Mostly I was wondering if there was a way to do this in one operation.

> Though, I don’t see why you can’t maintain a hash of all the lines  
> instead  
> of having to remove lines from the log file. Its never a good idea to  
> muck  
> about with log files.

hmmm…I suppose I could read the file and write out ones I recorded  
with a notation so I skip those in the future. I’ll have to think about  
that.

Thanks