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)
