changes

早期freebsd实现

	Major changes between "less" versions 123 and 170

* New option -j allows target lines to be positioned anywhere on screen.

* New option -S truncates displayed line at the screen width,
  rather than wrapping onto the next line.

* New option -y limits amount of forward scroll.

* New option -T specifies a "tags" file.

* Non-printable, non-control characters are displayed in octal.
  Such characters, as well as control characters, are displayed 
  in blinking mode.

* New command -+ sets an option to its default.
* New command -- sets an option to the opposite of its default.

* Lesskey file may have a string appended to a key's action,
  which acts as though typed in after the command.

* New commands ESC-^F and ESC-^B match arbitrary types of brackets.

* New command F monitors a growing file (like "tail -f").

* New command | pipes a section of the input file into a shell command.

* New command :x directly jumps to a file in the command line list.

* Search commands have been enhanced and reorganized:
	n	Repeat search, same direction.
	N	Repeat search, opposite direction.
	ESC-/	Search forward thru file boundaries
	ESC-?	Search backward thru file boundaries
	ESC-n	Repeat search thru file boundaries, same direction.
	ESC-N	Repeat search thru file boundaries, opposite direction.
  Special character * causes search to search thru file boundaries.
  Special character @ causes search to begin at start/end of file list.

* Examining a new file adds it to the command line list.
  A list of files, or an expression which matches more than one file,
  may be examined; all of them are added to the command line list.

* Environment variables LESSCHARSET and LESSCHARDEF can define
  a non-ASCII character set.

* Partial support for MSDOS, including options -R for repainting screen
  on quit, -v/-V to select video mode, and -W to change window size.


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	Major changes between "less" versions 97 and 123

* New option (-N) causes line numbers to be displayed in the
  text of the file (like vi "set nu").

* New option (-?) prints help message immediately.

* New option (-r) displays "raw" control characters, without
  mapping them to ^X notation.

* New option (-f) forces less to open non-regular files
  (directories, etc).

* New option (-k) can be used to specify lesskey files by name.

* New option (-y) can be used to set a forward scroll limit
  (like -h sets a backward scroll limit).

* File marks (set by the m command) are now preserved when a new
  file is edited.  The ' command can thus be used to switch files.

* New command ESC-/ searches all files (on the command line) 
  for a pattern.

* New command ESC-n repeats previous search, spanning files.

* The N command has been changed to repeat the previous search
  in the reverse direction.  The old N command is still available 
  via :n.

* New command ESC-N repeats previous search in the reverse
  direction and spanning files.

* 8 bit characters are now supported.  A new option (-g) can be 
  used to strip off the eighth bit (the previous behavior).

* Options which take a following string (like -t) may now
  optionally have a space between the option letter and the string.

* Six new commands { } ( ) [ and ] can be used to match
  brackets of specific types, similar to vi % command.

* New commands z and w move forward/backward one window and
  simultaneously set the window size.

* Prompt string expansion now has %L for line number of the last
  line in the file, and %E for the name of the editor.
  Also, % escapes which refer to a line (b=bottom, t=top, etc.)
  can use j for the jump target line.

* New environment variable LESSEDIT can be used to tailor the
  command string passed to the editor by the v command.

* Examining a file which was previously examined will return
  to the same position in the file.

* A "%" is expanded to the current filename and a "#" to the 
  previous filename, in both shell commands and the E command.
  (Previously % worked only in shell commands and # worked 
  only in the E command.)

* New command ":ta" is equivalent to "-t".

* New command "s" is equivalent to "-l".

* The - command may be followed by "+X" to revert to the default
  for option X, or "-X" to get the opposite of the default.

* Lesskey files may now include characters after the action as
  extra input to be parsed after the action; for example:
  "toggle-option X" to toggle a specific option X.