Class: File

Inherits:
Object
  • Object
show all
Defined in:
lib/rexec/reverse_io.rb

Constant Summary collapse

REVERSE_BUFFER_SIZE = 
128

Instance Method Summary collapse

Instance Method Details

#read_reverse(length) ⇒ Object

Read a chunk of data and then move the file pointer backwards.

Calling this function multiple times will return new data and traverse the file backwards.



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# File 'lib/rexec/reverse_io.rb', line 12

def read_reverse(length)
  offset = tell
  
  if offset == 0
    return nil
  end
  
  start = [0, offset-length].max
  
  seek(start, IO::SEEK_SET)
  
  buf = read(offset-start)
  
  seek(start, IO::SEEK_SET)
  
  return buf
end

#reverse_each_line(sep_string = $/, &block) ⇒ Object

Similar to each_line but works in reverse. Don’t forget to call seek_end before you start!



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# File 'lib/rexec/reverse_io.rb', line 61

def reverse_each_line(sep_string=$/, &block)
  line = reverse_gets(sep_string)
  
  while line != nil
    yield line
    
    line = reverse_gets(sep_string)
  end
end

#reverse_gets(sep_string = $/) ⇒ Object

This function is very similar to gets but it works in reverse.

You can use it to efficiently read a file line by line backwards.

It returns nil when there are no more lines.



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# File 'lib/rexec/reverse_io.rb', line 37

def reverse_gets(sep_string=$/)
  end_pos = tell
  
  offset = nil
  buf = ""
  
  while offset == nil
    chunk = read_reverse(REVERSE_BUFFER_SIZE)
    return (buf == "" ? nil : buf) if chunk == nil
    
    buf = chunk + buf
    
    offset = buf.rindex(sep_string)
  end
  
  line = buf[offset...buf.size].sub(sep_string, "")
  
  seek((end_pos - buf.size) + offset, IO::SEEK_SET)
  
  return line
end

#seek_end ⇒ Object

Seek to the end of the file



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# File 'lib/rexec/reverse_io.rb', line 4

def seek_end
  seek(0, IO::SEEK_END)
end