Less
NAME
less - opposite of more
SYNOPSIS
less -?
less -V
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 movement 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 special 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 displayed, 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 displayed, 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-[
Scroll horizontally left N characters, default 8. This
behaves best if you also set the -S option (chop
lines).
ESC-]
Scroll horizontally right 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). (Warning: 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.
(Warning: 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 brackets.
] Like }, but applies to square brackets rather than
curly brackets.
ESC-^F
Followed by two characters, acts like {, but uses the
two characters 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 characters 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. Followed 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
' command 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 pattern. N defaults to 1. The pattern is a
regular expression, as recognized by ed. The search
starts at the second line displayed (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 current screen, but don't move to the first
match (KEEP current 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 displayed 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 pattern. If the previous search was modified by
^N, the search is made for the N-th line NOT containing
the pattern. If the previous 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 crossing 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.
^X^V or E
Same as :e. Warning: some systems use ^V as a special
literalization 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 command 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 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
numeric or string-valued options.
_ (Underscore.) Followed by one of the command line
option letters (see below), this will print a message
describing the current 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 neither 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 examined 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 indicate beginning or end of
file respectively. If <m> is . or newline, 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 example, 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
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: "-\?".)
-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 allocated. The -B option
disables this automatic allocation of buffers for
pipes, so that only the number of buffers specified by
the -b option are used. 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 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 single 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 warning 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 highlight 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 uppercase 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 occurrence 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 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. 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 display 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 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
Specifies a tags file to be used instead of "tags".
-u Causes backspaces and carriage returns to be treated as
printable 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 specially: 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 boldface
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 underlined can be searched
for if neither -u nor -U is in effect.
-V Displays the version number of less.
-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 clearing 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 compatibility 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
automatically changes to 36 lines.
-- A command line argument of "--" marks the end of option
arguments. Any arguments following this are
interpreted as filenames. 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 initial 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), certain 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
literally by preceding it with the "literal" character,
either ^V or ^A. A backslash itself may also be entered
literally by entering two backslashes.
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 cursor one word to the left.
^RIGHTARROW [ ESC-w or ESC-RIGHTARROW ]
(That is, CONTROL and RIGHTARROW simultaneously.) Move
the cursor 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.
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 character 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 simply an executable
program (or shell script), which writes the contents of the
file to a different file, called the replacement file. The
contents of the replacement file are then displayed in place
of the contents 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 replacement filename,
less uses the original file, as normal. The input
preprocessor 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 program, 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 original 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 starting 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 replacement
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 replacement 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 previous 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 normal 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 represents 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
character 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 character 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 character 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 ordinary 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 specifies the line whose byte offset
is to be used. If the character 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 bottom
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 evaluated. 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 "Standard input".
?f%f .?ltLine %lt:?pt%pt\%:?btByte %bt:-...
This prompt would print the filename, if known. The
filename is followed 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, followed 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 reference, 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. (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 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.
LESSEDIT
Editor prototype string (used for the v command). See
discussion under PROMPTS.
LESSKEY
Name of the default lesskey(1) file.
LESSOPEN
Command line to invoke the (optional) input-
preprocessor.
LESSSECURE
Runs less in "secure" mode. See discussion under
SECURITY.
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 ALSO
lesskey(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 terminals, search highlighting is disabled
by default to avoid possible problems.
In certain cases, when search highlighting is enabled and a
search pattern begins with a ^, more text than the matching
string may be highlighted.
On some systems, setlocale claims that 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@3do.com