Table of Contents
less - opposite of more
less -?
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]...
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.
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-) 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 RIGHTARROW, 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). (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. 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 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.
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
On MS-DOS, you don't need
the quotes, but you should replace any percent 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 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.
- --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 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.
- -"
- 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 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.
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. 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 character in Unix to something other
than ^U, that character is used instead of ^U.
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.
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 "-".
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>".
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.
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 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 discussion 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 command 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 completion.
- 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).
lesskey(1)
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 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
(c) 1984,1985,1989,1994,1995,1996 Mark Nudelman
Comments to: markn@fog.net
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