vlfi/README.org

* View Large Files

Emacs minor mode that allows viewing, editing and searching large
files in batches.  Batch size can be adjusted on the fly and bounds
the memory that is to be used for operations on the file.

This is development version of the GNU ELPA [[http://elpa.gnu.org/packages/vlf][vlf.el]] package.  Here's
what it does in a nutshell:

- regular expression search on whole file (in constant memory
  determined by current batch size)
- chunk editing (if size has changed, saving is done in constant
  memory determined by current batch size)
- occur like indexing
- options to jump to beginning, end or arbitrary file chunk
- ability to jump/insert given number of batches at once
- newly added content is acknowledged if file has changed size
  meanwhile
- automatic scrolling of batches
- as VLF is minor mode, font locking and functionality of the
  respective major mode is also present
- VLF is added as an option when opening large files

GNU Emacs 23 and 24 are supported.

* Overview and tips

M-x vlf PATH-TO-FILE

** Unicode

Emacs' Unicode support is leveraged so you'll not see bare bytes but
characters decoded as if file is normally opened.  This holds for
editing, search and indexing.

** 32-bit GNU Emacs

Regular Emacs integers are used, so if you use 32-bit Emacs without
bignum support and have really huge file (with size beyond the maximum
integer value), VLF will probably not quite work.

** Memory control
*vlf-batch-size* bounds the memory used for all operations.

* Detail usage

** Applicability

You can control when vlf-mode is invoked or offered as choice with the
*vlf-application* customization option.  By default it will offer VLF
when opening large files.  There are also options to never use it (you
can still call *vlf* command explicitly); to use it without asking for
large files or to invoke it on all files.  Here's example setup such
that vlf-mode automatically launches for large files:

#+BEGIN_EXAMPLE
(custom-set-variables
 '(vlf-application 'dont-ask))
#+END_EXAMPLE

** Keymap

All VLF operations are grouped under the *C-c C-v* prefix by default.
Here's example how to add another prefix (*C-x v*):

#+BEGIN_EXAMPLE
(eval-after-load "vlf"
  '(define-key vlf-prefix-map "\C-xv" vlf-mode-map))
#+END_EXAMPLE

** Control batch size
*C-c C-v +* and *C-c C-v -* control current batch size by factors
of 2.

You can also set by hand local variable *vlf-batch-size* and then
refresh with *C-c C-v g*.

** Move around
*C-c C-v n* and *C-c C-v p* move batch by batch.  With positive
prefix argument they move prefix number of batches.  With negative -
append prefix number of batches.
*C-c C-v SPC* displays batch starting from current point.
*C-c C-v [* and *C-c C-v ]* take you to the beginning and end of file
respectively.
*C-c C-v j* jumps to given chunk.  To see where you are in file and
how many chunks there are (using the current batch size), look at the
parenthesized part of the buffer name, batch size is also indicated at
the end.

** Search whole file
*C-c C-v s* and *C-c C-v r* search forward and backward respectively
over the whole file.  This is done batch by batch so if you have
really huge file - you'd better set somewhat bigger batch size
beforehand.

** Occur over whole file
*C-c C-v o* builds index for given regular expression just like
*M-x occur*.  It does this batch by batch over the whole file.  Note
that even if you prematurely stop it with *C-g*, it will still show
index of what's found so far.

** Jump to line
*C-c C-v l* jumps to given line in file.  This is done by searching
from the beginning, so again the bigger current batch size, the
quicker.  With negative argument, lines are counted from the end of
file.

** Edit and save

If editing doesn't change size of the chunk, only this chunk is saved.
Otherwise the remaining part of the file is adjusted batch by batch,
so again you'd better have bigger current batch size.