less - Options

Options, Line editing and Language support for the Less command.

Options
       Most options may be changed while less is running, via the "-" command.
       
       Most options may be given in one of two forms: either a	dash  followed
       by  a  single  letter, or two dashes followed by a long option name.  A
       long option name may be abbreviated as  long  as	 the  abbreviation  is
       unambiguous.  For example, --quit-at-eof may be abbreviated --quit, but
       not --qui, since both --quit-at-eof and --quiet begin with --qui.  Some
       long  option names are in uppercase, such as --QUIT-AT-EOF, as distinct
       from --quit-at-eof.  Such option names need only have their first  let-
       ter  capitalized; the remainder of the name may be in either case.  For
       example, --Quit-at-eof is equivalent to --QUIT-AT-EOF.

       Options are also taken from the environment variable "LESS".  For exam-
       ple, to avoid typing "less -options ..." each time less is invoked, you
       might tell csh:

       setenv LESS "-options"

       or if you use sh:

       LESS="-options"; export LESS

       On MS-DOS, you don't need the quotes, but you should replace  any  per-
       cent signs in the options string by double percent signs.

       The  environment variable is parsed before the command line, so command
       line options override the LESS  environment  variable.	If  an	option
       appears	in  the LESS variable, it can be reset to its default value on
       the command line by beginning the command line option with "-+".

       For options like -P or -D which take a following string, a dollar  sign
       ($)  must be used to signal the end of the string.  For example, to set
       two -D options on MS-DOS, you must have a  dollar  sign	between	 them,
       like this:

       LESS="-Dn9.1$-Ds4.1"


       -? or --help
	      This  option displays a summary of the commands accepted by less
	      (the same as the h  command).   (Depending  on  how  your	 shell
	      interprets  the  question mark, it may be necessary to quote the
	      question mark, thus: "-\?".)

       -a or --search-skip-screen
	      Causes searches to start after the last line  displayed  on  the
	      screen,  thus  skipping  all  lines displayed on the screen.  By
	      default, searches start at the second line  on  the  screen  (or
	      after the last found line; see the -j option).

       -bn or --buffers=n
	      Specifies	 the  amount  of  buffer  space less will use for each
	      file, in units of kilobytes (1024 bytes).	  By  default  64K  of
	      buffer  space  is used for each file (unless the file is a pipe;
	      see the -B option).  The -b  option  specifies  instead  that  n
	      kilobytes of buffer space should be used for each file.  If n is
	      -1, buffer space is unlimited; that is, the entire file is  read
	      into memory.

       -B or --auto-buffers
	      By default, when data is read from a pipe, buffers are allocated
	      automatically as needed.	If a large amount of data is read from
	      the  pipe,  this	can cause a large amount of memory to be allo-
	      cated.  The -B option  disables  this  automatic	allocation  of
	      buffers  for  pipes,  so	that  only 64K (or the amount of space
	      specified by the -b option) is used for the pipe.	 Warning:  use
	      of  -B  can  result  in  erroneous  display, since only the most
	      recently viewed part of the file is kept in memory; any  earlier
	      data is lost.

       -c or --clear-screen
	      Causes  full  screen  repaints  to  be painted from the top line
	      down.  By default, full screen repaints are  done	 by  scrolling
	      from the bottom of the screen.

       -C or --CLEAR-SCREEN
	      The -C option is like -c, but the screen is cleared before it is
	      repainted.

       -d or --dumb
	      The -d option suppresses the error message normally displayed if
	      the  terminal is dumb; that is, lacks some important capability,
	      such as the ability to clear the screen or scroll backward.  The
	      -d  option  does	not otherwise change the behavior of less on a
	      dumb terminal.

       -Dxcolor or --color=xcolor
	      [MS-DOS only] Sets the color of the text displayed.  x is a sin-
	      gle  character  which  selects  the  type of text whose color is
	      being set: n=normal, s=standout, d=bold, u=underlined,  k=blink.
	      color  is	 a  pair  of numbers separated by a period.  The first
	      number selects the foreground color and the second  selects  the
	      background  color of the text.  A single number N is the same as
	      N.0.

       -e or --quit-at-eof
	      Causes less to automatically exit the  second  time  it  reaches
	      end-of-file.   By	 default, the only way to exit less is via the
	      "q" command.

       -E or --QUIT-AT-EOF
	      Causes less to automatically exit the first time it reaches end-
	      of-file.

       -f or --force
	      Forces non-regular files to be opened.  (A non-regular file is a
	      directory or a device special file.)  Also suppresses the	 warn-
	      ing message when a binary file is opened.	 By default, less will
	      refuse to open non-regular files.

       -F or --quit-if-one-screen
	      Causes less to automatically exit if the entire file can be dis-
	      played on the first screen.

       -g or --hilite-search
	      Normally,	 less  will highlight ALL strings which match the last
	      search command.  The -g option changes this  behavior  to	 high-
	      light  only  the	particular  string which was found by the last
	      search command.  This can cause less to run somewhat faster than
	      the default.

       -G or --HILITE-SEARCH
	      The  -G  option  suppresses all highlighting of strings found by
	      search commands.

       -hn or ---max-back-scroll=n
	      Specifies a maximum number of lines to scroll backward.	If  it
	      is necessary to scroll backward more than n lines, the screen is
	      repainted in a forward direction instead.	 (If the terminal does
	      not have the ability to scroll backward, -h0 is implied.)

       -i or --ignore-case
	      Causes searches to ignore case; that is, uppercase and lowercase
	      are considered identical.	 This option is ignored if any	upper-
	      case  letters appear in the search pattern; in other words, if a
	      pattern contains uppercase letters, then that  search  does  not
	      ignore case.

       -I or --IGNORE-CASE
	      Like  -i,	 but searches ignore case even if the pattern contains
	      uppercase letters.

       -jn or --jump-target=n
	      Specifies a line on the screen where the "target" line is to  be
	      positioned.   A  target line is the object of a text search, tag
	      search, jump to a line number, jump to  a	 file  percentage,  or
	      jump  to	a  marked position.  The screen line is specified by a
	      number: the top line on the screen is 1, the next is 2,  and  so
	      on.   The	 number	 may be negative to specify a line relative to
	      the bottom of the screen: the bottom line on the screen  is  -1,
	      the  second to the bottom is -2, and so on.  If the -j option is
	      used, searches begin at the line immediately  after  the	target
	      line.   For  example,  if	 "-j4" is used, the target line is the
	      fourth line on the screen, so searches begin at the  fifth  line
	      on the screen.

       -J or --status-column
	      Displays	a  status  column at the left edge of the screen.  The
	      status column shows the lines that matched the  current  search.
	      The  status  column  is  also  used if the -w or -W option is in
	      effect.

       -kfilename or --lesskey-file=filename
	      Causes less to open and interpret the named file	as  a  lesskey
	      (1) file.	 Multiple -k options may be specified.	If the LESSKEY
	      or LESSKEY_SYSTEM environment variable is set, or if  a  lesskey
	      file is found in a standard place (see KEY BINDINGS), it is also
	      used as a lesskey file.

       -m or --long-prompt
	      Causes less to prompt verbosely (like more),  with  the  percent
	      into the file.  By default, less prompts with a colon.

       -M or --LONG-PROMPT
	      Causes less to prompt even more verbosely than more.

       -n or --line-numbers
	      Suppresses  line numbers.	 The default (to use line numbers) may
	      cause less to run more slowly in some cases, especially  with  a
	      very  large  input  file.	  Suppressing line numbers with the -n
	      option will avoid this problem.  Using line numbers  means:  the
	      line number will be displayed in the verbose prompt and in the =
	      command, and the v command will pass the current line number  to
	      the  editor  (see	 also  the  discussion	of LESSEDIT in PROMPTS
	      below).

       -N or --LINE-NUMBERS
	      Causes a line number to be displayed at the  beginning  of  each
	      line in the display.

       -ofilename or --log-file=filename
	      Causes  less  to copy its input to the named file as it is being
	      viewed.  This applies only when the input file is a pipe, not an
	      ordinary	file.	If  the file already exists, less will ask for
	      confirmation before overwriting it.

       -Ofilename or --LOG-FILE=filename
	      The -O option is like -o, but it will overwrite an existing file
	      without asking for confirmation.

	      If  no log file has been specified, the -o and -O options can be
	      used from within less to specify a log  file.   Without  a  file
	      name, they will simply report the name of the log file.  The "s"
	      command is equivalent to specifying -o from within less.

       -ppattern or --pattern=pattern
	      The -p option on the command line is  equivalent	to  specifying
	      +/pattern;  that	is, it tells less to start at the first occur-
	      rence of pattern in the file.

       -Pprompt or --prompt=prompt
	      Provides a way to tailor the three prompt	 styles	 to  your  own
	      preference.   This  option  would	 normally  be  put in the LESS
	      environment variable, rather than being typed in with each  less
	      command.	 Such  an option must either be the last option in the
	      LESS variable, or be terminated by a dollar sign.	 -Ps  followed
	      by  a  string changes the default (short) prompt to that string.
	      -Pm changes the medium (-m) prompt.  -PM changes the  long  (-M)
	      prompt.	-Ph  changes  the  prompt  for	the  help screen.  -P=
	      changes the message printed by the = command.  -Pw  changes  the
	      message  printed while waiting for data (in the F command).  All
	      prompt strings consist of a  sequence  of	 letters  and  special
	      escape  sequences.  See the section on PROMPTS for more details.

       -q or --quiet or --silent
	      Causes moderately "quiet" operation: the terminal	 bell  is  not
	      rung if an attempt is made to scroll past the end of the file or
	      before the beginning of the file.	 If the terminal has a "visual
	      bell",  it  is  used  instead.  The bell will be rung on certain
	      other errors, such as typing an invalid character.  The  default
	      is to ring the terminal bell in all such cases.

       -Q or --QUIET or --SILENT
	      Causes  totally  "quiet"	operation:  the terminal bell is never
	      rung.

       -r or --raw-control-chars
	      Causes "raw" control characters to be displayed.	The default is
	      to  display  control  characters	using  the caret notation; for
	      example, a control-A (octal 001) is displayed as "^A".  Warning:
	      when the -r option is used, less cannot keep track of the actual
	      appearance of the screen (since this depends on how  the	screen
	      responds to each type of control character).  Thus, various dis-
	      play problems may result, such as long lines being split in  the
	      wrong place.

       -R or --RAW-CONTROL-CHARS
	      Like  -r, but tries to keep track of the screen appearance where
	      possible.	 This works only if the input consists of normal  text
	      and  possibly  some  ANSI	 "color"  escape  sequences, which are
	      sequences of the form:

		   ESC [ ... m

	      where the "..." is zero or more characters other than "m".   For
	      the  purpose  of keeping track of screen appearance, all control
	      characters and all ANSI color escape sequences  are  assumed  to
	      not  move	 the  cursor.  You can make less think that characters
	      other than "m" can end ANSI color escape	sequences  by  setting
	      the environment variable LESSANSIENDCHARS to the list of charac-
	      ters which can end a color escape sequence.

       -s or --squeeze-blank-lines
	      Causes consecutive blank lines to	 be  squeezed  into  a	single
	      blank line.  This is useful when viewing nroff output.

       -S or --chop-long-lines
	      Causes  lines  longer than the screen width to be chopped rather
	      than folded.  That is, the remainder of a long  line  is	simply
	      discarded.   The default is to fold long lines; that is, display
	      the remainder on the next line.

       -ttag or --tag=tag
	      The -t option, followed immediately by a TAG, will edit the file
	      containing  that tag.  For this to work, tag information must be
	      available; for example, there may	 be  a	file  in  the  current
	      directory called "tags", which was previously built by ctags (1)
	      or an equivalent command.	 If the environment variable LESSGLOB-
	      ALTAGS  is set, it is taken to be the name of a command compati-
	      ble with global (1), and that command is executed	 to  find  the
	      tag.  (See http://www.gnu.org/software/global/global.html).  The
	      -t option may also be specified from within less	(using	the  -
	      command)	as a way of examining a new file.  The command ":t" is
	      equivalent to specifying -t from within less.

       -Ttagsfile or --tag-file=tagsfile
	      Specifies a tags file to be used instead of "tags".

       -u or --underline-special
	      Causes backspaces and carriage returns to be treated  as	print-
	      able  characters;	 that  is,  they are sent to the terminal when
	      they appear in the input.

       -U or --UNDERLINE-SPECIAL
	      Causes backspaces, tabs and carriage returns to  be  treated  as
	      control  characters;  that  is, they are handled as specified by
	      the -r option.

	      By default, if neither -u nor  -U	 is  given,  backspaces	 which
	      appear  adjacent	to  an	underscore  character are treated spe-
	      cially: the underlined text is displayed	using  the  terminal's
	      hardware	underlining capability.	 Also, backspaces which appear
	      between two identical  characters	 are  treated  specially:  the
	      overstruck  text	is printed using the terminal's hardware bold-
	      face capability.	Other backspaces are deleted, along  with  the
	      preceding character.  Carriage returns immediately followed by a
	      newline are deleted.  other  carriage  returns  are  handled  as
	      specified	 by the -r option.  Text which is overstruck or under-
	      lined can be searched for if neither -u nor -U is in effect.

       -V or --version
	      Displays the version number of less.

       -w or --hilite-unread
	      Temporarily highlights the first	"new"  line  after  a  forward
	      movement of a full page.	The first "new" line is the line imme-
	      diately following the line  previously  at  the  bottom  of  the
	      screen.  Also highlights the target line after a g or p command.
	      The highlight is removed at the next command which causes	 move-
	      ment.   The  entire line is highlighted, unless the -J option is
	      in effect, in which case only the status column is  highlighted.

       -W or --HILITE-UNREAD
	      Like -w, but temporarily highlights the first new line after any
	      forward movement command larger than one line.

       -xn,... or --tabs=n,...
	      Sets tab stops.  If only one n is specified, tab stops  are  set
	      at  multiples  of n.  If multiple values separated by commas are
	      specified, tab stops are set at those positions, and  then  con-
	      tinue  with  the	same  spacing  as  the last two.  For example,
	      -x9,17 will set tabs at positions	 9,  17,  25,  33,  etc.   The
	      default for n is 8.

       -X or --no-init
	      Disables sending the termcap initialization and deinitialization
	      strings to the terminal.	This is	 sometimes  desirable  if  the
	      deinitialization	string does something unnecessary, like clear-
	      ing the screen.

       --no-keypad
	      Disables sending the keypad initialization and  deinitialization
	      strings to the terminal.	This is sometimes useful if the keypad
	      strings make the numeric keypad behave in an undesirable manner.

       -yn or --max-forw-scroll=n
	      Specifies a maximum number of lines to scroll forward.  If it is
	      necessary to scroll forward more than n  lines,  the  screen  is
	      repainted	 instead.   The -c or -C option may be used to repaint
	      from the top of the screen if desired.  By default, any  forward
	      movement causes scrolling.

       -[z]n or --window=n
	      Changes  the  default  scrolling	window	size  to n lines.  The
	      default is one screenful.	 The z and w commands can also be used
	      to  change the window size.  The "z" may be omitted for compati-
	      bility with more.	 If the number n is negative, it  indicates  n
	      lines  less  than	 the current screen size.  For example, if the
	      screen is 24 lines, -z-4 sets the scrolling window to 20	lines.
	      If the screen is resized to 40 lines, the scrolling window auto-
	      matically changes to 36 lines.

       -"cc or --quotes=cc
	      Changes the filename quoting character.  This may	 be  necessary
	      if  you are trying to name a file which contains both spaces and
	      quote characters.	 Followed by a single character, this  changes
	      the  quote  character to that character.	Filenames containing a
	      space should then be surrounded by that character rather than by
	      double  quotes.	Followed  by  two characters, changes the open
	      quote to the first character, and the close quote to the	second
	      character.  Filenames containing a space should then be preceded
	      by the open quote character and  followed	 by  the  close	 quote
	      character.   Note	 that  even  after  the	 quote	characters are
	      changed, this option remains -" (a dash  followed	 by  a	double
	      quote).

       -~ or --tilde
	      Normally lines after end of file are displayed as a single tilde
	      (~).  This option causes lines after end of file to be displayed
	      as blank lines.

       -# or --shift
	      Specifies the default number of positions to scroll horizontally
	      in the RIGHTARROW and LEFTARROW commands.	 If the number	speci-
	      fied  is	zero,  it  sets the default number of positions to one
	      half of the screen width.

       --     A command line argument of "--" marks the end  of	 option	 argu-
	      ments.   Any  arguments  following this are interpreted as file-
	      names.  This can be useful when viewing a file whose name begins
	      with a "-" or "+".

       +      If  a  command  line option begins with +, the remainder of that
	      option is taken to be an initial command to less.	 For  example,
	      +G  tells	 less  to start at the end of the file rather than the
	      beginning, and +/xyz tells it to start at the  first  occurrence
	      of  "xyz"	 in  the file.	As a special case, + acts like
	      +g; that is, it starts the display at the specified line
	      number  (however,	 see  the caveat under the "g" command above).
	      If the option starts with ++, the	 initial  command  applies  to
	      every  file being viewed, not just the first one.	 The + command
	      described previously may also be used to set (or change) an ini-
	      tial command for every file.

LINE EDITING

       When  entering command line at the bottom of the screen (for example, a
       filename for the :e command, or the pattern for a search command), cer-
       tain  keys  can	be used to manipulate the command line.	 Most commands
       have an alternate form in [ brackets ] which can be used if a key  does
       not  exist  on a particular keyboard.  (The bracketed forms do not work
       in the MS-DOS version.)	Any of these special keys may be entered  lit-
       erally  by  preceding it with the "literal" character, either ^V or ^A.
       A backslash itself may also be entered literally by entering two	 back-
       slashes.

       LEFTARROW [ ESC-h ]
	      Move the cursor one space to the left.

       RIGHTARROW [ ESC-l ]
	      Move the cursor one space to the right.

       ^LEFTARROW [ ESC-b or ESC-LEFTARROW ]
	      (That  is, CONTROL and LEFTARROW simultaneously.)	 Move the cur-
	      sor one word to the left.

       ^RIGHTARROW [ ESC-w or ESC-RIGHTARROW ]
	      (That is, CONTROL and RIGHTARROW simultaneously.)	 Move the cur-
	      sor one word to the right.

       HOME [ ESC-0 ]
	      Move the cursor to the beginning of the line.

       END [ ESC-$ ]
	      Move the cursor to the end of the line.

       BACKSPACE
	      Delete  the  character  to the left of the cursor, or cancel the
	      command if the command line is empty.

       DELETE or [ ESC-x ]
	      Delete the character under the cursor.

       ^BACKSPACE [ ESC-BACKSPACE ]
	      (That is, CONTROL and  BACKSPACE	simultaneously.)   Delete  the
	      word to the left of the cursor.

       ^DELETE [ ESC-X or ESC-DELETE ]
	      (That  is,  CONTROL and DELETE simultaneously.)  Delete the word
	      under the cursor.

       UPARROW [ ESC-k ]
	      Retrieve the previous command line.

       DOWNARROW [ ESC-j ]
	      Retrieve the next command line.

       TAB    Complete the partial filename to the left of the cursor.	If  it
	      matches  more than one filename, the first match is entered into
	      the command line.	 Repeated  TABs	 will  cycle  thru  the	 other
	      matching filenames.  If the completed filename is a directory, a
	      "/" is appended to the filename.	(On MS-DOS systems, a  "\"  is
	      appended.)   The	environment variable LESSSEPARATOR can be used
	      to specify a different character to append to a directory	 name.

       BACKTAB [ ESC-TAB ]
	      Like, TAB, but cycles in the reverse direction thru the matching
	      filenames.

       ^L     Complete the partial filename to the left of the cursor.	If  it
	      matches more than one filename, all matches are entered into the
	      command line (if they fit).

       ^U (Unix and OS/2) or ESC (MS-DOS)
	      Delete the entire command line, or cancel	 the  command  if  the
	      command line is empty.  If you have changed your line-kill char-
	      acter in Unix to something other than ^U, that character is used
	      instead of ^U.
KEY BINDINGS

       You  may define your own less commands by using the program lesskey (1)
       to create a lesskey file.  This file specifies a set  of	 command  keys
       and  an	action	associated with each key.  You may also use lesskey to
       change the line-editing keys (see LINE EDITING), and to set environment
       variables.   If the environment variable LESSKEY is set, less uses that
       as the name of the lesskey file.	 Otherwise, less looks in  a  standard
       place  for  the lesskey file: On Unix systems, less looks for a lesskey
       file called "$HOME/.less".  On MS-DOS and Windows systems,  less	 looks
       for  a lesskey file called "$HOME/_less", and if it is not found there,
       then looks for a lesskey file called "_less" in any directory specified
       in  the	PATH  environment variable.  On OS/2 systems, less looks for a
       lesskey file called "$HOME/less.ini", and if  it	 is  not  found,  then
       looks  for  a lesskey file called "less.ini" in any directory specified
       in the INIT environment variable, and if it not found there, then looks
       for  a lesskey file called "less.ini" in any directory specified in the
       PATH environment variable.   See	 the  lesskey  manual  page  for  more
       details.

       A  system-wide lesskey file may also be set up to provide key bindings.
       If a key is defined in both a local lesskey file and in the system-wide
       file,  key bindings in the local file take precedence over those in the
       system-wide file.  If the environment variable LESSKEY_SYSTEM  is  set,
       less uses that as the name of the system-wide lesskey file.  Otherwise,
       less looks in a standard place for the  system-wide  lesskey  file:  On
       Unix  systems,  the system-wide lesskey file is /usr/local/etc/sysless.
       (However, if less was built with a  different  sysconf  directory  than
       /usr/local/etc, that directory is where the sysless file is found.)  On
       MS-DOS and Windows systems, the system-wide lesskey  file  is  c:\_sys-
       less.  On OS/2 systems, the system-wide lesskey file is c:\sysless.ini.

INPUT PREPROCESSOR

       You may define an "input preprocessor" for less.	 Before less  opens  a
       file, it first gives your input preprocessor a chance to modify the way
       the contents of the file are displayed.	An input preprocessor is  sim-
       ply  an executable program (or shell script), which writes the contents
       of the file to a different file, called the replacement file.  The con-
       tents  of  the replacement file are then displayed in place of the con-
       tents of the original file.  However, it will appear to the user as  if
       the  original  file  is opened; that is, less will display the original
       filename as the name of the current file.


       An input preprocessor receives one command line argument, the  original
       filename,  as  entered  by  the user.  It should create the replacement
       file, and when finished, print the name of the replacement file to  its
       standard	 output.  If the input preprocessor does not output a replace-
       ment filename, less uses the original file, as normal.  The input  pre-
       processor  is  not  called  when	 viewing standard input.  To set up an
       input preprocessor, set the LESSOPEN environment variable to a  command
       line  which  will  invoke  your	input preprocessor.  This command line
       should include one  occurrence  of  the	string	"%s",  which  will  be
       replaced	 by  the  filename  when  the  input  preprocessor  command is
       invoked.

       When less closes a file opened in such a way, it will call another pro-
       gram,  called  the  input  postprocessor, which may perform any desired
       clean-up action (such as	 deleting  the	replacement  file  created  by
       LESSOPEN).  This program receives two command line arguments, the orig-
       inal filename as entered by the user, and the name of  the  replacement
       file.   To set up an input postprocessor, set the LESSCLOSE environment
       variable to a command line which will invoke your input	postprocessor.
       It  may	include	 two  occurrences  of  the  string  "%s"; the first is
       replaced with the original name of the file and	the  second  with  the
       name of the replacement file, which was output by LESSOPEN.

       For  example, on many Unix systems, these two scripts will allow you to
       keep files in compressed format, but still let less view them directly:

       lessopen.sh:
	    #! /bin/sh
	    case "$1" in
	    *.Z) uncompress -c $1  >/tmp/less.$$  2>/dev/null
		 if [ -s /tmp/less.$$ ]; then
		      echo /tmp/less.$$
		 else
		      rm -f /tmp/less.$$
		 fi
		 ;;
	    esac

       lessclose.sh:
	    #! /bin/sh
	    rm $2

       To  use these scripts, put them both where they can be executed and set
       LESSOPEN="lessopen.sh %s",  and	LESSCLOSE="lessclose.sh %s %s".	  More
       complex	LESSOPEN  and LESSCLOSE scripts may be written to accept other
       types of compressed files, and so on.

       It is also possible to set up an input preprocessor to  pipe  the  file
       data  directly to less, rather than putting the data into a replacement
       file.  This avoids the need to decompress the entire file before start-
       ing to view it.	An input preprocessor that works this way is called an
       input pipe.  An input pipe, instead of writing the name of  a  replace-
       ment  file  on  its  standard output, writes the entire contents of the
       replacement file on its standard output.	 If the input  pipe  does  not
       write  any characters on its standard output, then there is no replace-
       ment file and less uses the original file, as normal.  To use an	 input
       pipe,  make  the first character in the LESSOPEN environment variable a
       vertical bar (|) to signify that the input  preprocessor	 is  an	 input
       pipe.

       For  example, on many Unix systems, this script will work like the pre-
       vious example scripts:

       lesspipe.sh:
	    #! /bin/sh
	    case "$1" in
	    *.Z) uncompress -c $1  2>/dev/null
		 ;;
	    esac

       To  use	this  script,  put  it	where  it  can	be  executed  and  set
       LESSOPEN="|lesspipe.sh  %s".   When  an input pipe is used, a LESSCLOSE
       postprocessor can be used, but it is usually not necessary since	 there
       is no replacement file to clean up.  In this case, the replacement file
       name passed to the LESSCLOSE postprocessor is "-".

NATIONAL CHARACTER SETS

       There are three types of characters in the input file:

       normal characters
	      can be displayed directly to the screen.

       control characters
	      should not be displayed directly, but are expected to  be	 found
	      in ordinary text files (such as backspace and tab).

       binary characters
	      should  not  be  displayed  directly  and are not expected to be
	      found in text files.

       A "character set" is simply a description of which characters are to be
       considered  normal,  control,  and binary.  The LESSCHARSET environment
       variable may be used to select a character set.	 Possible  values  for
       LESSCHARSET are:

       ascii  BS,  TAB, NL, CR, and formfeed are control characters, all chars
	      with values between 32 and 126 are normal, and  all  others  are
	      binary.

       iso8859
	      Selects  an  ISO 8859 character set.  This is the same as ASCII,
	      except characters between 160 and	 255  are  treated  as	normal
	      characters.

       latin1 Same as iso8859.

       latin9 Same as iso8859.

       dos    Selects a character set appropriate for MS-DOS.

       ebcdic Selects an EBCDIC character set.

       IBM-1047
	      Selects  an  EBCDIC  character set used by OS/390 Unix Services.
	      This is the EBCDIC analogue of latin1.  You get similar  results
	      by setting either LESSCHARSET=IBM-1047 or LC_CTYPE=en_US in your
	      environment.

       koi8-r Selects a Russian character set.

       next   Selects a character set appropriate for NeXT computers.

       utf-8  Selects the UTF-8 encoding of the ISO 10646 character set.
       In special cases, it may be desired to tailor less to use  a  character
       set  other  than	 the ones definable by LESSCHARSET.  In this case, the
       environment variable LESSCHARDEF can be used to define a character set.
       It  should be set to a string where each character in the string repre-
       sents one character in the character set.  The character	 "."  is  used
       for a normal character, "c" for control, and "b" for binary.  A decimal
       number may be used for repetition.  For example, "bccc4b."  would  mean
       character  0  is	 binary,  1,  2	 and  3 are control, 4, 5, 6 and 7 are
       binary, and 8 is normal.	 All characters after the last are taken to be
       the  same  as  the  last,  so characters 9 through 255 would be normal.
       (This is an example, and does not necessarily represent any real	 char-
       acter set.)

       This  table  shows the value of LESSCHARDEF which is equivalent to each
       of the possible values for LESSCHARSET:

	    ascii     8bcccbcc18b95.b
	    dos	      8bcccbcc12bc5b95.b.
	    ebcdic    5bc6bcc7bcc41b.9b7.9b5.b..8b6.10b6.b9.7b
		      9.8b8.17b3.3b9.7b9.8b8.6b10.b.b.b.
	    IBM-1047  4cbcbc3b9cbccbccbb4c6bcc5b3cbbc4bc4bccbc
		      191.b
	    iso8859   8bcccbcc18b95.33b.
	    koi8-r    8bcccbcc18b95.b128.
	    latin1    8bcccbcc18b95.33b.
	    next      8bcccbcc18b95.bb125.bb

       If  neither  LESSCHARSET nor LESSCHARDEF is set, but the string "UTF-8"
       is found in the LC_ALL, LC_TYPE or LANG environment variables, then the
       default character set is utf-8.

       If  that	 string	 is  not found, but your system supports the setlocale
       interface, less will use setlocale  to  determine  the  character  set.
       setlocale  is  controlled  by  setting the LANG or LC_CTYPE environment
       variables.

       Finally, if the setlocale interface is also not available, the  default
       character set is latin1.

       Control	and  binary  characters	 are  displayed	 in  standout (reverse
       video).	Each such character is displayed in caret notation if possible
       (e.g.  ^A for control-A).  Caret notation is used only if inverting the
       0100 bit results in a normal printable character.  Otherwise, the char-
       acter  is displayed as a hex number in angle brackets.  This format can
       be changed by setting the LESSBINFMT environment variable.   LESSBINFMT
       may begin with a "*" and one character to select the display attribute:
       "*k" is blinking, "*d" is bold, "*u" is underlined, "*s"	 is  standout,
       and  "*n"  is  normal.  If LESSBINFMT does not begin with a "*", normal
       attribute is assumed.  The remainder of LESSBINFMT is  a	 string	 which
       may  include one printf-style escape sequence (a % followed by x, X, o,
       d, etc.).  For example, if LESSBINFMT is	 "*u[%x]",  binary  characters
       are  displayed  in  underlined hexadecimal surrounded by brackets.  The
       default if no LESSBINFMT is specified is "*s<%X>".

PROMPTS

       The -P option allows you to tailor the prompt to your preference.   The
       string  given  to  the  -P option replaces the specified prompt string.
       Certain characters in the string are interpreted specially.  The prompt
       mechanism  is  rather complicated to provide flexibility, but the ordi-
       nary user need not understand the details of constructing  personalized
       prompt strings.

       A  percent sign followed by a single character is expanded according to
       what the following character is:

       %bX    Replaced by the byte offset into the current input file.	The  b
	      is followed by a single character (shown as X above) which spec-
	      ifies the line whose byte offset is to be used.  If the  charac-
	      ter  is a "t", the byte offset of the top line in the display is
	      used, an "m" means use the middle line, a "b" means use the bot-
	      tom  line,  a "B" means use the line just after the bottom line,
	      and a "j" means use the "target" line, as specified  by  the  -j
	      option.

       %B     Replaced by the size of the current input file.

       %c     Replaced by the column number of the text appearing in the first
	      column of the screen.

       %dX    Replaced by the page number of a line in the  input  file.   The
	      line to be used is determined by the X, as with the %b option.

       %D     Replaced	by  the	 number of pages in the input file, or equiva-
	      lently, the page number of the last line in the input file.

       %E     Replaced by the name of the editor (from the VISUAL  environment
	      variable,	 or  the  EDITOR environment variable if VISUAL is not
	      defined).	 See the discussion of the LESSEDIT feature below.

       %f     Replaced by the name of the current input file.

       %i     Replaced by the index of the current file in the list  of	 input
	      files.

       %lX    Replaced	by  the	 line number of a line in the input file.  The
	      line to be used is determined by the X, as with the %b option.

       %L     Replaced by the line number of the last line in the input	 file.

       %m     Replaced by the total number of input files.

       %pX    Replaced	by  the	 percent into the current input file, based on
	      byte offsets.  The line used is determined by the X as with  the
	      %b option.
       %PX    Replaced	by  the	 percent into the current input file, based on
	      line numbers.  The line used is determined by the X as with  the
	      %b option.

       %s     Same as %B.

       %t     Causes  any  trailing spaces to be removed.  Usually used at the
	      end of the string, but may appear anywhere.

       %x     Replaced by the name of the next input file in the list.

       If any item is unknown (for example, the file size if input is a pipe),
       a question mark is printed instead.

       The  format  of	the  prompt string can be changed depending on certain
       conditions.  A question mark followed by a single character  acts  like
       an  "IF":  depending  on the following character, a condition is evalu-
       ated.  If the condition is true, any characters following the  question
       mark  and  condition  character,	 up  to	 a period, are included in the
       prompt.	If the condition is false, such characters are	not  included.
       A  colon appearing between the question mark and the period can be used
       to establish an "ELSE": any characters between the colon and the period
       are  included  in  the string if and only if the IF condition is false.
       Condition characters (which follow a question mark) may be:

       ?a     True if any characters have been included in the prompt so  far.

       ?bX    True if the byte offset of the specified line is known.

       ?B     True if the size of current input file is known.

       ?c     True if the text is horizontally shifted (%c is not zero).

       ?dX    True if the page number of the specified line is known.

       ?e     True if at end-of-file.

       ?f     True  if	there is an input filename (that is, if input is not a
	      pipe).

       ?lX    True if the line number of the specified line is known.

       ?L     True if the line number of the last line in the file is known.

       ?m     True if there is more than one input file.

       ?n     True if this is the first prompt in a new input file.

       ?pX    True if the percent into the current input file, based  on  byte
	      offsets, of the specified line is known.

       ?PX    True  if	the percent into the current input file, based on line
	      numbers, of the specified line is known.

       ?s     Same as "?B".

       ?x     True if there is a next input file  (that	 is,  if  the  current
	      input file is not the last one).

       Any  characters	other  than  the  special  ones (question mark, colon,
       period, percent, and backslash) become literally part  of  the  prompt.
       Any  of	the special characters may be included in the prompt literally
       by preceding it with a backslash.

      Some examples:

       ?f%f:Standard input.

       This prompt prints the filename, if known; otherwise the string	"Stan-
       dard input".

       ?f%f .?ltLine %lt:?pt%pt\%:?btByte %bt:-...

       This  prompt  would print the filename, if known.  The filename is fol-
       lowed by the line number, if known, otherwise  the  percent  if	known,
       otherwise  the  byte  offset  if	 known.	 Otherwise, a dash is printed.
       Notice how each question mark has a matching  period,  and  how	the  %
       after the %pt is included literally by escaping it with a backslash.

       ?n?f%f .?m(file %i of %m) ..?e(END) ?x- Next\: %x..%t

       This  prints  the  filename if this is the first prompt in a file, fol-
       lowed by the "file N of N" message if there  is	more  than  one	 input
       file.   Then,  if  we are at end-of-file, the string "(END)" is printed
       followed by the name of the next file, if there is one.	 Finally,  any
       trailing spaces are truncated.  This is the default prompt.  For refer-
       ence, here are the defaults for	the  other  two	 prompts  (-m  and  -M
       respectively).	Each  is  broken  into	two lines here for readability
       only.

       ?n?f%f .?m(file %i of %m) ..?e(END) ?x- Next\: %x.:
	    ?pB%pB\%:byte %bB?s/%s...%t

      ?f%f .?n?m(file %i of %m) ..?ltlines %lt-%lb?L/%L. :
	    byte %bB?s/%s. .?e(END) ?x- Next\: %x.:?pB%pB\%..%t

       And here is the default message produced by the = command:

       ?f%f .?m(file %i of %m) .?ltlines %lt-%lb?L/%L. .
	    byte %bB?s/%s. ?e(END) :?pB%pB\%..%t

       The prompt expansion features are also used for another purpose: if  an
       environment  variable LESSEDIT is defined, it is used as the command to
       be executed when the v command is  invoked.   The  LESSEDIT  string  is
       expanded	 in the same way as the prompt strings.	 The default value for
       LESSEDIT is:

	    %E ?lm+%lm. %f

       Note that this expands to the editor name, followed by a + and the line
       number,	followed by the file name.  If your editor does not accept the
       "+linenumber" syntax, or has other differences  in  invocation  syntax,
       the LESSEDIT variable can be changed to modify this default.

SECURITY

       When  the  environment  variable LESSSECURE is set to 1, less runs in a
       "secure" mode.  This means these features are disabled:

	      !	     the shell command

	      |	     the pipe command

	      :e     the examine command.

	      v	     the editing command

	      s	 -o  log files

	      -k     use of lesskey files

	      -t     use of tags files

		     metacharacters in filenames, such as *

		     filename completion (TAB, ^L)

       Less can also be compiled to be permanently in "secure" mode.

ENVIRONMENT VARIABLES

       Environment variables may be specified either in the system environment
       as  usual,  or  in  a  lesskey  (1) file.  If environment variables are
       defined in more than one place, variables defined in  a	local  lesskey
       file  take precedence over variables defined in the system environment,
       which take precedence over variables defined in the system-wide lesskey
       file.

       COLUMNS
	      Sets the number of columns on the screen.	 Takes precedence over
	      the number of columns specified by the TERM variable.   (But  if
	      you  have	 a  windowing  system  which  supports	TIOCGWINSZ  or
	      WIOCGETD, the window system's idea  of  the  screen  size	 takes
	      precedence over the LINES and COLUMNS environment variables.)

       EDITOR The name of the editor (used for the v command).

       HOME   Name  of	the user's home directory (used to find a lesskey file
	      on Unix and OS/2 systems).

       HOMEDRIVE, HOMEPATH
	      Concatenation of the HOMEDRIVE and  HOMEPATH  environment	 vari-
	      ables is the name of the user's home directory if the HOME vari-
	      able is not set (only in the Windows version).

       INIT   Name of the user's init directory (used to find a	 lesskey  file
	      on OS/2 systems).

       LANG   Language for determining the character set.

       LC_CTYPE
	      Language for determining the character set.

       LESS   Options which are passed to less automatically.

       LESSANSIENDCHARS
	      Characters  which	 are  assumed  to  end	an  ANSI  color escape
	      sequence (default "m").

       LESSBINFMT
	      Format for displaying non-printable, non-control characters.

       LESSCHARDEF
	      Defines a character set.

       LESSCHARSET
	      Selects a predefined character set.

       LESSCLOSE
	      Command line to invoke the (optional) input-postprocessor.

       LESSECHO
	      Name of the lessecho program (default "lessecho").  The lessecho
	      program  is needed to expand metacharacters, such as * and ?, in
	      filenames on Unix systems.

       LESSEDIT
	      Editor prototype string (used for the v command).	  See  discus-
	      sion under PROMPTS.

       LESSGLOBALTAGS
	      Name  of	the command used by the -t option to find global tags.
	      Normally should be set to "global" if your system has the global
	      (1) command.  If not set, global tags are not used.

       LESSKEY
	      Name of the default lesskey(1) file.

       LESSKEY_SYSTEM
	      Name of the default system-wide lesskey(1) file.

       LESSMETACHARS
	      List  of characters which are considered "metacharacters" by the
	      shell.

       LESSMETAESCAPE
	      Prefix which less will add before each metacharacter in  a  com-
	      mand  sent  to the shell.	 If LESSMETAESCAPE is an empty string,
	      commands containing metacharacters will not  be  passed  to  the
	      shell.

       LESSOPEN
	      Command line to invoke the (optional) input-preprocessor.

       LESSSECURE
	      Runs less in "secure" mode.  See discussion under SECURITY.

       LESSSEPARATOR
	      String  to  be  appended to a directory name in filename comple-
	      tion.

       LINES  Sets the number of lines on the screen.  Takes  precedence  over
	      the number of lines specified by the TERM variable.  (But if you
	      have a windowing system which supports TIOCGWINSZ	 or  WIOCGETD,
	      the  window  system's  idea  of the screen size takes precedence
	      over the LINES and COLUMNS environment variables.)

       PATH   User's search path (used to find a lesskey file  on  MS-DOS  and
	      OS/2 systems).

       SHELL  The  shell  used	to execute the ! command, as well as to expand
	      filenames.

       TERM   The type of terminal on which less is being run.

       VISUAL The name of the editor (used for the v command).

less does not have to read the entire input file before starting, so with large input files it starts up faster than text editors like vi.

"To teach is not difficult. But you must be careful not to teach dumb things, that's all. You must not teach them fashion, you must teach them how to create" ~ Wolfgang Weingart

Related:

lesskey -
echo - Display message on screen
tee - Redirect output to multiple files
The less home page (Mark Nudelman)


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