Read "current line" from a file?

ruby-talk
1

All,

Given an IO object, you can get the “next” line with #gets, right?

Given an IO object, you can get the “current” line with #X, right? Please?

I know it’s not a common operation, but I would like tobe able to do it.

···

–
Gavin Sinclair Software Engineer
Sydney, Australia Soyabean Software Pty Ltd

2

Hello

Yo can go back one line and gets

class File
def current
self.lineno=self.lineno-1
self.gets
end
end

hope it helps and it’s what you are looking for

bye

···

On Thu 24 Oct 2002 11:57, Gavin Sinclair wrote:

All,

Given an IO object, you can get the “next” line with #gets, right?

Given an IO object, you can get the “current” line with #X, right? Please?

I know it’s not a common operation, but I would like tobe able to do it.

–
Gavin Sinclair Software Engineer
Sydney, Australia Soyabean Software Pty Ltd

–
Javier Fontan Muiños
jfontan@cesga.es
CESGA, Supercomputing Center of Galicia

3

Hi –

All,

Given an IO object, you can get the “next” line with #gets, right?

Given an IO object, you can get the “current” line with #X, right? Please?

I know it’s not a common operation, but I would like tobe able to do it.

Do you mean a kind of one-line lookahead? I had occasion to do that
somewhere recently, and did:

class File
def ungets(str)
seek(pos - str.size,0)
end

# One-line lookahead.
def next_line
  line = gets
  ungets(line) if line
  line
end

end

David

···

On Thu, 24 Oct 2002, Gavin Sinclair wrote:

–
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web: http://pirate.shu.edu/~blackdav

4

Hi,

Given an IO object, you can get the “next” line with #gets, right?

Given an IO object, you can get the “current” line with #X, right? Please?

What about this?

class IO
module Backing
def gets(rs = $/)
@backing = super
end
def last
@backing
end
end
end

STDIN.extend(IO::Backing)
p STDIN.gets
p STDIN.last

···

At Thu, 24 Oct 2002 18:57:49 +0900, Gavin Sinclair wrote:

–
Nobu Nakada

5

Hi –

···

On Thu, 24 Oct 2002, Javier Fontan wrote:

Hello

Yo can go back one line and gets

class File
def current
self.lineno=self.lineno-1
self.gets
end
end

I can’t get that to work. Do you have a working example?

David

–
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web: http://pirate.shu.edu/~blackdav

6

Hi –

All,

Given an IO object, you can get the “next” line with #gets, right?

Given an IO object, you can get the “current” line with #X, right? Please?

I know it’s not a common operation, but I would like tobe able to do it.

Do you mean a kind of one-line lookahead? I had occasion to do that
somewhere recently, and did:

class File
def ungets(str)
seek(pos - str.size,0)
end

# One-line lookahead.
def next_line
  line = gets
  ungets(line) if line
  line
end

end

David

Hmmm… I might give that a go. This is the sort of thing I’m trying to do.
I’ve got the following code:

  file.reverse_each do |line|
    if line =~ /Published/
      timestamp = collect_timestamp(line)
      line = file.gets && file.gets
      unless line.nil?
        backend_id = collect_backend_id(line)
        ...
      end
    end
  end

And I’d like to refactor it to:

  file.reverse_each do |line|
    if line =~ /Published/
      timestamp, backend_id = collect_data(file)
    end
  end

  def collect_data(file)
    timestamp = collect_timestamp(file.current_line)
    line = file.gets && file.gets
    unless line.nil?
      backend_id = collect_backend_id(line)
      ...
    end
  end

File#reverse_each is a nifty method I wrote to process a file in reverse line
order. I was (obviously) hoping that IO/File would have a buffer of the
current line that it can share with me! If I have to hack it, then I don’t
really achieve anything pretty.

Thanks,
Gavin

···

From: dblack@candle.superlink.net

On Thu, 24 Oct 2002, Gavin Sinclair wrote:

7

Hi,

Given an IO object, you can get the “next” line with #gets, right?

Given an IO object, you can get the “current” line with #X, right? Please?

What about this?

class IO
module Backing
def gets(rs = $/)
@backing = super
end
def last
@backing
end
end
end

STDIN.extend(IO::Backing)
p STDIN.gets
p STDIN.last

That’s quite nice. I pronounce this the best solution so far :slight_smile:

Nobu Nakada

Gavin

···

From: nobu.nokada@softhome.net

At Thu, 24 Oct 2002 18:57:49 +0900, > Gavin Sinclair wrote:

8

Wouldn’t you need:
@backing = super(rs)
to be correct?

-austin
– Austin Ziegler, austin@halostatue.ca on 2002.10.24 at 13.07.23

···

On Thu, 24 Oct 2002 21:35:55 +0900, nobu.nokada@softhome.net wrote:

class IO
module Backing
def gets(rs = $/)
@backing = super
end
def last
@backing
end
end
end

STDIN.extend(IO::Backing)
p STDIN.gets
p STDIN.last

9

Wouldn't you need:
    @backing = super(rs)
to be correct?

You have found one reason why `super' is a keyword and not a method :slight_smile:

`super' without () propagate the arguments given to the methods.

Guy Decoux