LESS(1)LESS(1)NAMEless - opposite of more
SYNOPSISless -?
less--help
less-V
less--version
less [-[+]aBcCdeEfgGiImMnNqQrsSuUVwX]
[-b bufs] [-h lines] [-j line] [-k keyfile]
[-{oO} logfile] [-p pattern] [-P prompt] [-t tag]
[-T tagsfile] [-x tab] [-y lines] [-[z] lines]
[+[+]cmd] [--] [filename]...
DESCRIPTION
Less is a program similar to more (1), but which allows backward move‐
ment in the file as well as forward movement. Also, 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 (1). Less uses
termcap (or terminfo on some systems), so it can run on a variety of
terminals. There is even limited support for hardcopy terminals. (On
a hardcopy terminal, lines which should be printed at the top of the
screen are prefixed with a caret.)
Commands are based on both more and vi. Commands may be preceded by a
decimal number, called N in the descriptions below. The number is used
by some commands, as indicated.
COMMANDS
In the following descriptions, ^X means control-X. ESC stands for the
ESCAPE key; for example ESC-v means the two character sequence
"ESCAPE", then "v".
h or H Help: display a summary of these commands. If you forget all
the other commands, remember this one.
SPACE or ^V or f or ^F
Scroll forward N lines, default one window (see option -z
below). If N is more than the screen size, only the final
screenful is displayed. Warning: some systems use ^V as a spe‐
cial literalization character.
z Like SPACE, but if N is specified, it becomes the new window
size.
ESC-SPACE
Like SPACE, but scrolls a full screenful, even if it reaches
end-of-file in the process.
RETURN or ^N or e or ^E or j or ^J
Scroll forward N lines, default 1. The entire N lines are dis‐
played, even if N is more than the screen size.
d or ^D
Scroll forward N lines, default one half of the screen size. If
N is specified, it becomes the new default for subsequent d and
u commands.
b or ^B or ESC-v
Scroll backward N lines, default one window (see option -z
below). If N is more than the screen size, only the final
screenful is displayed.
w Like ESC-v, but if N is specified, it becomes the new window
size.
y or ^Y or ^P or k or ^K
Scroll backward N lines, default 1. The entire N lines are dis‐
played, even if N is more than the screen size. Warning: some
systems use ^Y as a special job control character.
u or ^U
Scroll backward N lines, default one half of the screen size.
If N is specified, it becomes the new default for subsequent d
and u commands.
ESC-) or RIGHTARROW
Scroll horizontally right N characters, default 8. This behaves
best if you also set the -S option (chop lines). Note that if
you wish to enter a number N, you must use ESC-), not RIGHTAR‐
ROW, because the arrow is taken to be a line editing command
(see the LINE EDITING section).
ESC-( or LEFTARROW
Scroll horizontally left N characters, default 8.
r or ^R or ^L
Repaint the screen.
R Repaint the screen, discarding any buffered input. Useful if
the file is changing while it is being viewed.
F Scroll forward, and keep trying to read when the end of file is
reached. Normally this command would be used when already at
the end of the file. It is a way to monitor the tail of a file
which is growing while it is being viewed. (The behavior is
similar to the "tail -f" command.)
g or < or ESC-<
Go to line N in the file, default 1 (beginning of file). (Warn‐
ing: this may be slow if N is large.)
G or > or ESC->
Go to line N in the file, default the end of the file. (Warn‐
ing: this may be slow if N is large, or if N is not specified
and standard input, rather than a file, is being read.)
p or % Go to a position N percent into the file. N should be between 0
and 100.
{ If a left curly bracket appears in the top line displayed on the
screen, the { command will go to the matching right curly
bracket. The matching right curly bracket is positioned on the
bottom line of the screen. If there is more than one left curly
bracket on the top line, a number N may be used to specify the
N-th bracket on the line.
} If a right curly bracket appears in the bottom line displayed on
the screen, the } command will go to the matching left curly
bracket. The matching left curly bracket is positioned on the
top line of the screen. If there is more than one right curly
bracket on the top line, a number N may be used to specify the
N-th bracket on the line.
( Like {, but applies to parentheses rather than curly brackets.
) Like }, but applies to parentheses rather than curly brackets.
[ Like {, but applies to square brackets rather than curly brack‐
ets.
] Like }, but applies to square brackets rather than curly brack‐
ets.
ESC-^F Followed by two characters, acts like {, but uses the two char‐
acters as open and close brackets, respectively. For example,
"ESC ^F < >" could be used to go forward to the > which matches
the < in the top displayed line.
ESC-^B Followed by two characters, acts like }, but uses the two char‐
acters as open and close brackets, respectively. For example,
"ESC ^B < >" could be used to go backward to the < which matches
the > in the bottom displayed line.
m Followed by any lowercase letter, marks the current position
with that letter.
' (Single quote.) Followed by any lowercase letter, returns to
the position which was previously marked with that letter. Fol‐
lowed by another single quote, returns to the position at which
the last "large" movement command was executed. Followed by a ^
or $, jumps to the beginning or end of the file respectively.
Marks are preserved when a new file is examined, so the ' com‐
mand can be used to switch between input files.
^X^X Same as single quote.
/pattern
Search forward in the file for the N-th line containing the pat‐
tern. N defaults to 1. The pattern is a regular expression, as
recognized by ed. The search starts at the second line dis‐
played (but see the -a and -j options, which change this).
Certain characters are special if entered at the beginning of
the pattern; they modify the type of search rather than become
part of the pattern:
^N or !
Search for lines which do NOT match the pattern.
^E or *
Search multiple files. That is, if the search reaches
the END of the current file without finding a match, the
search continues in the next file in the command line
list.
^F or @
Begin the search at the first line of the FIRST file in
the command line list, regardless of what is currently
displayed on the screen or the settings of the -a or -j
options.
^K Highlight any text which matches the pattern on the cur‐
rent screen, but don't move to the first match (KEEP cur‐
rent position).
^R Don't interpret regular expression metacharacters; that
is, do a simple textual comparison.
?pattern
Search backward in the file for the N-th line containing the
pattern. The search starts at the line immediately before the
top line displayed.
Certain characters are special as in the / command:
^N or !
Search for lines which do NOT match the pattern.
^E or *
Search multiple files. That is, if the search reaches
the beginning of the current file without finding a
match, the search continues in the previous file in the
command line list.
^F or @
Begin the search at the last line of the last file in the
command line list, regardless of what is currently dis‐
played on the screen or the settings of the -a or -j
options.
^K As in forward searches.
^R As in forward searches.
ESC-/pattern
Same as "/*".
ESC-?pattern
Same as "?*".
n Repeat previous search, for N-th line containing the last pat‐
tern. If the previous search was modified by ^N, the search is
made for the N-th line NOT containing the pattern. If the pre‐
vious search was modified by ^E, the search continues in the
next (or previous) file if not satisfied in the current file.
If the previous search was modified by ^R, the search is done
without using regular expressions. There is no effect if the
previous search was modified by ^F or ^K.
N Repeat previous search, but in the reverse direction.
ESC-n Repeat previous search, but crossing file boundaries. The
effect is as if the previous search were modified by *.
ESC-N Repeat previous search, but in the reverse direction and cross‐
ing file boundaries.
ESC-u Undo search highlighting. Turn off highlighting of strings
matching the current search pattern. If highlighting is already
off because of a previous ESC-u command, turn highlighting back
on. Any search command will also turn highlighting back on.
(Highlighting can also be disabled by toggling the -G option; in
that case search commands do not turn highlighting back on.)
:e [filename]
Examine a new file. If the filename is missing, the "current"
file (see the :n and :p commands below) from the list of files
in the command line is re-examined. A percent sign (%) in the
filename is replaced by the name of the current file. A pound
sign (#) is replaced by the name of the previously examined
file. However, two consecutive percent signs are simply
replaced with a single percent sign. This allows you to enter a
filename that contains a percent sign in the name. Similarly,
two consecutive pound signs are replaced with a single pound
sign. The filename is inserted into the command line list of
files so that it can be seen by subsequent :n and :p commands.
If the filename consists of several files, they are all inserted
into the list of files and the first one is examined. If the
filename contains one or more spaces, the entire filename should
be enclosed in double quotes (also see the -" option).
^X^V or E
Same as :e. Warning: some systems use ^V as a special literal‐
ization character. On such systems, you may not be able to use
^V.
:n Examine the next file (from the list of files given in the com‐
mand line). If a number N is specified, the N-th next file is
examined.
:p Examine the previous file in the command line list. If a number
N is specified, the N-th previous file is examined.
:x Examine the first file in the command line list. If a number N
is specified, the N-th file in the list is examined.
= or ^G or :f
Prints some information about the file being viewed, including
its name and the line number and byte offset of the bottom line
being displayed. If possible, it also prints the length of the
file, the number of lines in the file and the percent of the
file above the last displayed line.
- Followed by one of the command line option letters (see below),
this will change the setting of that option and print a message
describing the new setting. If the option letter has a numeric
value (such as -b or -h), or a string value (such as -P or -t),
a new value may be entered after the option letter. If no new
value is entered, a message describing the current setting is
printed and nothing is changed.
-+ Followed by one of the command line option letters (see below),
this will reset the option to its default setting and print a
message describing the new setting. (The "-+X" command does the
same thing as "-+X" on the command line.) This does not work
for string-valued options.
-- Followed by one of the command line option letters (see below),
this will reset the option to the "opposite" of its default set‐
ting and print a message describing the new setting. (The "--X"
command does the same thing as "-X" on the command line.) This
does not work for numeric or string-valued options.
_ (Underscore.) Followed by one of the command line option let‐
ters (see below), this will print a message describing the cur‐
rent setting of that option. The setting of the option is not
changed.
+cmd Causes the specified cmd to be executed each time a new file is
examined. For example, +G causes less to initially display each
file starting at the end rather than the beginning.
V Prints the version number of less being run.
q or Q or :q or :Q or ZZ
Exits less.
The following four commands may or may not be valid, depending on your
particular installation.
v Invokes an editor to edit the current file being viewed. The
editor is taken from the environment variable VISUAL if defined,
or EDITOR if VISUAL is not defined, or defaults to "vi" if nei‐
ther VISUAL nor EDITOR is defined. See also the discussion of
LESSEDIT under the section on PROMPTS below.
! shell-command
Invokes a shell to run the shell-command given. A percent sign
(%) in the command is replaced by the name of the current file.
A pound sign (#) is replaced by the name of the previously exam‐
ined file. "!!" repeats the last shell command. "!" with no
shell command simply invokes a shell. On Unix systems, the
shell is taken from the environment variable SHELL, or defaults
to "sh". On MS-DOS and OS/2 systems, the shell is the normal
command processor.
| <m> shell-command
<m> represents any mark letter. Pipes a section of the input
file to the given shell command. The section of the file to be
piped is between the first line on the current screen and the
position marked by the letter. <m> may also be ^ or $ to indi‐
cate beginning or end of file respectively. If <m> is . or new‐
line, the current screen is piped.
s filename
Save the input to a file. This only works if the input is a
pipe, not an ordinary file.
OPTIONS
Command line options are described below. Most options may be changed
while less is running, via the "-" command.
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 on the
command line by beginning the command line option with "-+".
For options like -P which take a following string, a dollar sign ($)
may be used to signal the end of the string.
-? 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: "-\?".)
--help Same as -?.
-a 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 Specifies the number of buffers less will use for each file.
Buffers are 1K, and by default 10 buffers are used for each file
(except if the file is a pipe; see the -B option). The number n
specifies a different number of buffers to use.
-B 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 buf‐
fers for pipes, so that only the number of buffers specified by
the -b option are used. Warning: use of -B can result in erro‐
neous display, since only the most recently viewed part of the
file is kept in memory; any earlier data is lost.
-c 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 The -C option is like -c, but the screen is cleared before it is
repainted.
-d 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
[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 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 Causes less to automatically exit the first time it reaches end-
of-file.
-f 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.
-g 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 The -G option suppresses all highlighting of strings found by
search commands.
-hn 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 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 Like -i, but searches ignore case even if the pattern contains
uppercase letters.
-jn 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.
-kfilename
Causes less to open and interpret the named file as a lesskey
(1) file. Multiple -k options may be specified. If the LESSKEY
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 Causes less to prompt verbosely (like more), with the percent
into the file. By default, less prompts with a colon.
-M Causes less to prompt even more verbosely than more.
-n 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 Causes a line number to be displayed at the beginning of each
line in the display.
-ofilename
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
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
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
Provides a way to tailor the three prompt styles to your own
preference. This option would normally be put in the LESS envi‐
ronment variable, rather than being typed in with each less com‐
mand. 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. All prompt
strings consist of a sequence of letters and special escape
sequences. See the section on PROMPTS for more details.
-q 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 Causes totally "quiet" operation: the terminal bell is never
rung.
-r 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.
-s Causes consecutive blank lines to be squeezed into a single
blank line. This is useful when viewing nroff output.
-S 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 The -t option, followed immediately by a TAG, will edit the file
containing that tag. For this to work, there must be a file
called "tags" in the current directory, which was previously
built by the ctags (1) command. This option may also be speci‐
fied from within less (using the - command) as a way of examin‐
ing a new file. The command ":t" is equivalent to specifying -t
from within less.
-Ttagsfile
Specifies a tags file to be used instead of "tags".
-u 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 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 Displays the version number of less.
--version
Same as -V.
-w Causes blank lines to be used to represent lines past the end of
the file. By default, a tilde character (~) is used.
-xn Sets tab stops every n positions. The default for n is 8.
-X 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.
-yn 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 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.
-" 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).
-- 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, +<number> acts like
+<number>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) 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 "$HOME/.less". On MS-DOS systems, less looks for a lesskey
file called "$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.
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 The default character set. BS, TAB, NL, CR, and formfeed are
control characters, all chars with values between 127 and 255
are binary, and all others are normal.
latin1 Selects the ISO 8859/1 character set. latin-1 is the same as
ASCII, except characters between 161 and 255 are treated as nor‐
mal characters.
dos Selects a character set appropriate for MS-DOS.
koi8-r Selects a Russian character set.
next Selects a character set appropriate for NeXT computers.
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
latin1 8bcccbcc18b95.33b.
dos 8bcccbcc12bc5b95.b.
koi8-r 8bcccbcc18b95.b128.
next 8bcccbcc18b95.bb125.bb
If neither LESSCHARSET nor LESSCHARDEF is set, but your system supports
the setlocale interface, less will use setlocale to determine the char‐
acter set. setlocale is controlled by setting the LANG or LC_CTYPE
environment variables.
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 "*d<%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.
%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. 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.
?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 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) ..?ltline %lt?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) .?ltline %lt?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.
COLUMNS
Sets the number of columns on the screen. Takes precedence over
the number of columns specified by the TERM variable.
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 systems).
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.
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.
LESSKEY
Name of the default 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.
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).
SEE ALSOlesskey(1)WARNINGS
The = command and prompts (unless changed by -P) report the line number
of the line at the top of the screen, but the byte and percent of the
line at the bottom of the screen.
If the :e command is used to name more than one file, and one of the
named files has been viewed previously, the new files may be entered
into the list in an unexpected order.
On certain older terminals (the so-called "magic cookie" terminals),
search highlighting will cause an erroneous display. On such termi‐
nals, search highlighting is disabled by default to avoid possible
problems.
In certain cases, when search highlighting is enabled and a search pat‐
tern begins with a ^, more text than the matching string may be high‐
lighted.
On some systems, setlocale claims that ASCII characters 0 thru 31 are
control characters rather than binary characters. This causes less to
treat some binary files as ordinary, non-binary files. To workaround
this problem, set the environment variable LESSCHARSET to "ascii" (or
whatever character set is appropriate).
COPYRIGHT
Copyright (c) 1984,1985,1989,1994,1995,1996 Mark Nudelman
Comments to: markn@fog.net
Version 332: 22 Apr 97 LESS(1)
