Read last line of a file

[Shuaib Zahda]

Hi all

I was trying to find a method to read only the last line of a file. I
checked the the documentation and there is no such method.
Beside reading line after line and checking the the eof method. Is there
any faster or shorter way to do that.

Regards

 

[Gregory Seidman]

Hi all

I was trying to find a method to read only the last line of a file. I
checked the the documentation and there is no such method.
Beside reading line after line and checking the the eof method. Is there
any faster or shorter way to do that.

Depending on your platform, you might find that using popen with tail -1
will be the fastest and easiest way. Failing that, consider this:

last = File.open(myfile) { |f| f.extend(Enumerable).inject { |_,ln| ln } }

Regards

--Greg

 

[Xavier Noria]

I was trying to find a method to read only the last line of a file. I
checked the the documentation and there is no such method.
Beside reading line after line and checking the the eof method. Is
there
any faster or shorter way to do that.

In Perl there's File::ReadBackwards:

http://search.cpan.org/~uri/File-ReadBackwards-1.04/ReadBackwards.pm

The idea is that you put the file object in binmode and pick a chunk
of bytes towards the end of the file using for example

file.seek(-chunk_size_in_bytes, IO::SEEK_END)

and see whether the last (or last-but-one) line separator is there. If
it is not, step a bit backwards and try again.

-- fxn

 

[James Edward Gray II]

In Perl there's File::ReadBackwards:

http://search.cpan.org/~uri/File-ReadBackwards-1.04/ReadBackwards.pm

I ported this library as a solution to an old quiz:

http://rubyquiz.com/quiz64.html

It's a gem now, so you can do:

gem install elif

James Edward Gray II

 

[Xavier Noria]

I ported this library as a solution to an old quiz:

http://rubyquiz.com/quiz64.html

It's a gem now, so you can do:

gem install elif

Good!

 

[Robert Klemme]

Depending on your platform, you might find that using popen with tail -1
will be the fastest and easiest way. Failing that, consider this:

last = File.open(myfile) { |f| f.extend(Enumerable).inject { |_,ln| ln } }

You do not need the ".extend(Enumerable)" bit as an IO does already
include Enumerable:

$ ruby -e 'p Enumerable === $stdin'
true

Cheers

robert

 

[Gregory Seidman]

You do not need the ".extend(Enumerable)" bit as an IO does already
include Enumerable:

$ ruby -e 'p Enumerable === $stdin'
true

Ah, sorry, you are correct. For some reason I was thinking of MySQL result
sets.

Cheers
robert

--Greg

 

[Shuaib Zahda]

Hi
Sorry for posting late

I was trying to figure out how to use this method but I failed. Can u
please give me an example

 

[Lee Jarvis]

Hi
Sorry for posting late

I was trying to figure out how to use this method but I failed. Can u
please give me an example

It works just like File#each, except in reverse order..

http://elif.rubyforge.org/ for documentation.

You could also just do something like this..

File.readlines(file).reverse_each {

But of course, that reads the whole file into an array first, so I would
still to using elif.

Regards,
Lee

 

[James Edward Gray II]

I was trying to figure out how to use this method but I failed. Can u
please give me an example

require "elif"

last_line = Elif.open(path) { |f| f.gets }

James Edward Gray II

 

[Brian Adkins]

Hi all

I was trying to find a method to read only the last line of a file. I
checked the the documentation and there is no such method.
Beside reading line after line and checking the the eof method. Is there
any faster or shorter way to do that.

last_line = `tail -n 1 #{file_name}`

 

[Shuaib Zahda]

require "elif"

last_line = Elif.open(path) { |f| f.gets }

James Edward Gray II

Thanks it works. But when i used require "elif". My ruby did not
recognize its path. So i copied it into my local directory and ran it
fine. Is there any path issue that i have to tackle when i download new
package from gem. I am using ubuntu 7.10

Regards

 

[Shuaib Zahda]

From: Shuaib Zahda [mailto:[email protected]]
# Thanks it works. But when i used require "elif". My ruby did not
# recognize its path. So i copied it into my local directory and ran it
# fine. Is there any path issue that i have to tackle when i
# download new package from gem. I am using ubuntu 7.10

try,
require 'rubygems'

gems require rubygems to find themselves
require is change thereupon..

Thanks a lot. It works well. So, I can conclude that I have to call
rubygems then I call the elif.

Regards

 

[Peña, Botp]

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a2luZCByZWdhcmRzIC1ib3RwDQo=

 

[Peña, Botp]

From: James Edward Gray II [mailto:[email protected]]=20
# require "elif"
# last_line =3D Elif.open(path) { |f| f.gets }

cool.

wc reminds me, i'm looking for a gem that reverses the behaviour of =
string/collection/io/ traversals, like

#file reverse
require "in_reverse"
last_line =3D File.open(path).in_reverse { |f| f.gets }

#array reverse
%w(this is a test).each.in_reverse {|x| p x}
test
a
is
this

#string reverse
"this is a test".each_char.in_reverse {|c| p c; break if c=3D=3D"a"}
t
s
e
t

a

#
kind regards -botp

 

[James Edward Gray II]

wc reminds me, i'm looking for a gem that reverses the behaviour of =20=

string/collection/io/ traversals, like

#array reverse
%w(this is a test).each.in_reverse {|x| p x}
test
a
is
this

This can be hard to support for all iterators, but Array does have =20
reverse_each():

%w[this is a test].reverse_each { |word| puts word }

test
a
is
this
=3D> ["this", "is", "a", "test"]

James Edward Gray II=