LESS(1) LESS(1)
NAME
less - opposite of more (a filter for browsing text files)
SYNOPSIS
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]... more [options] page [options]
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. Warn- ing: some systems use ^V as a special literaliza- tion 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 Version 335: 03 Apr 1999 1 LESS(1) LESS(1) 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 Version 335: 03 Apr 1999 2 LESS(1) LESS(1) 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. Version 335: 03 Apr 1999 3 LESS(1) LESS(1) 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 con- taining the pattern. N defaults to 1. When invoked as less, the pattern is an extended regular expression. Otherwise, the pattern is a basic reg- ular 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 pat- tern. ^E or * Search multiple files. That is, if the search reaches the END of the current file without finding a match, the search contin- ues in the next file in the command line list. The * modifier is available when invoked as less only. ^F or @ Begin the search at the first line of the FIRST file in the command line list, regard- less of what is currently displayed on the screen or the settings of the -a or -j options. The @ modifier is available when invoked as less only. ^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 metachar- acters; that is, do a simple textual Version 335: 03 Apr 1999 4 LESS(1) LESS(1) comparison. ?pattern Search backward in the file for the N-th line con- taining 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 pat- tern. ^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 com- mand line list. ^F or @ Begin the search at the last line of the last file in the command line list, regard- less 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 modi- fied 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 direc- tion. ESC-n Repeat previous search, but crossing file bound- aries. The effect is as if the previous search were modified by *. Version 335: 03 Apr 1999 5 LESS(1) LESS(1) ESC-N Repeat previous search, but in the reverse direc- tion 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 pre- viously 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. Simi- larly, 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 spe- cial 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 Version 335: 03 Apr 1999 6 LESS(1) LESS(1) 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 set- ting. 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 noth- ing 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 mes- sage describing the new setting. (The "--X" com- mand 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 mes- sage 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. Version 335: 03 Apr 1999 7 LESS(1) LESS(1) ! 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 environ- ment variable SHELL, or defaults to "sh". On MS- DOS and OS/2 systems, the shell is the normal com- mand 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 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 environ- ment 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 or -D which take a following string, a dollar sign ($) must be used to signal the end of the string. For example, to set two -D options on MS-DOS, you must have a dollar sign between them, like this: Version 335: 03 Apr 1999 8 LESS(1) LESS(1) LESS="-Dn9.1$-Ds4.1" -? This option displays a summary of the commands accepted by less (the same as the h command). (Depending on how your shell interprets the ques- tion mark, it may be necessary to quote the ques- tion mark, thus: "-\?".) --help Same as -?. -a Causes searches to start after the last line dis- played on the screen, thus skipping all lines dis- played 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 speci- fies 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. Warn- ing: 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 causes the default prompt to include the basic directions ``[Press space to continue, 'q' to quit.]''. The -d option also causes the message ``[Press 'h' for instructions.]'' to be displayed when an invalid command is entered (nor- mally, the bell is rung). This option is useful in environments where users may not be experienced with pagers. -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, Version 335: 03 Apr 1999 9 LESS(1) LESS(1) 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-reg- ular 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 partic- ular string which was found by the last search com- mand. 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 back- ward. 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 pat- tern 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 Version 335: 03 Apr 1999 10 LESS(1) LESS(1) second to the bottom is -2, and so on. If the -j option is used, searches begin at the line immedi- ately 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 begin- ning 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 Version 335: 03 Apr 1999 11 LESS(1) LESS(1) 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 Version 335: 03 Apr 1999 12 LESS(1) LESS(1) 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 Temporarily highlights the first "new" line after a forward movement of a full page. The first "new" line is the line immediately following the line previously at the bottom of the screen. The high- light is removed at the next command which causes movement. -W Like -w, but temporarily highlights the first new line after any forward movement command larger than one line. -xn Sets tab stops every n positions. The default for n is 8. -X Disables sending the termcap initialization and Version 335: 03 Apr 1999 13 LESS(1) LESS(1) 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 for- ward. 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 indi- cates 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 automati- cally 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. Fol- lowed 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 char- acter. 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 remain- der of that option is taken to be an initial com- mand 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 dis- play 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. Version 335: 03 Apr 1999 14 LESS(1) LESS(1) 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 pat- tern for a search command), certain keys can be used to manipulate the command line. Most commands have an alter- nate 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. Version 335: 03 Apr 1999 15 LESS(1) LESS(1) 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 direc- tory, 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 com- mand if the command line is empty. If you have changed your line-kill character in Unix to some- thing 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 speci- fied 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 environ- ment 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. Version 335: 03 Apr 1999 16 LESS(1) LESS(1)
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 file- name, 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 environ- ment 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 origi- nal 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 ;; Version 335: 03 Apr 1999 17 LESS(1) LESS(1) esac lessclose.sh: #! /bin/sh rm $2 To use these scripts, put them both where they can be exe- cuted 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 pre- processor 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 Version 335: 03 Apr 1999 18 LESS(1) LESS(1) 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 charac- ters 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 32 and 126 are normal, and all oth- ers are binary. iso8859 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. latin1 Same as iso8859. dos Selects a character set appropriate for MS-DOS. ebcdic Selects an EBCDIC character set. koi8-r Selects a Russian character set. next Selects a character set appropriate for NeXT com- puters. In special cases, it may be desired to tailor less to use a character set other than the ones definable by LESS- CHARSET. In this case, the environment variable LESS- CHARDEF can be used to define a character set. It should be set to a string where each character in the string rep- resents 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 repeti- tion. 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 neces- sarily represent any real character set.) This table shows the value of LESSCHARDEF which is equiva- lent to each of the possible values for LESSCHARSET: ascii 8bcccbcc18b95.b dos 8bcccbcc12bc5b95.b. ebcdic 5bc6bcc7bcc41b.9b7.9b5.b..8b6.10b6.b9.7b 9.8b8.17b3.3b9.7b9.8b8.6b10.b.b.b. Version 335: 03 Apr 1999 19 LESS(1) LESS(1) iso8859 8bcccbcc18b95.33b. koi8-r 8bcccbcc18b95.b128. latin1 8bcccbcc18b95.33b. 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 vari- able. 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 LESS- BINFMT is "*u[%x]", binary characters are displayed in underlined hexadecimal surrounded by brackets. The default if no LESSBINFMT is specified is "*s<%X>".
PROMPTS
The -P option allows you to tailor the prompt to your preference. The string given to the -P option replaces the specified prompt string. Certain characters in the string are interpreted specially. The prompt mechanism is rather complicated to provide flexibility, but the ordi- nary user need not understand the details of constructing personalized prompt strings. A percent sign followed by a single character is expanded according to what the following character is: %bX Replaced by the byte offset into the current input file. The b is followed by a single character (shown as X above) which 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. Version 335: 03 Apr 1999 20 LESS(1) LESS(1) %dX Replaced by the page number of a line in the input file. The line to be used is determined by the X, as with the %b option. %D Replaced by the number of pages in the input file, or equivalently, the page number of the last line in the input file. %E Replaced by the name of the editor (from the VISUAL environment variable, or the EDITOR environment variable if VISUAL is not defined). See the dis- cussion 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 any- where. %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 sin- gle character acts like an "IF": depending on the follow- ing 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. Version 335: 03 Apr 1999 21 LESS(1) LESS(1) 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. ?dX True if the page number of the specified line is known. ?e True if at end-of-file. ?f True if there is an input filename (that is, if input is not a pipe). ?lX True if the line number of the specified line is known. ?L True if the line number of the last line in the file is known. ?m True if there is more than one input file. ?n True if this is the first prompt in a new input file. ?pX True if the percent into the current input file 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 Version 335: 03 Apr 1999 22 LESS(1) LESS(1) filename is followed by the line number, if known, other- wise 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 back- slash. ?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 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 com- mand 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 vari- able 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 Version 335: 03 Apr 1999 23 LESS(1) LESS(1) :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 sys- tem 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. Version 335: 03 Apr 1999 24 LESS(1) LESS(1) LESSCHARSET Selects a predefined character set. LESSCLOSE Command line to invoke the (optional) input-post- processor. LESSECHO Name of the lessecho program (default "lessecho"). The lessecho program is needed to expand metachar- acters, such as * and ?, in filenames on Unix sys- tems. 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 "metachar- acters" by the shell. LESSMETAESCAPE Prefix which less will add before each metacharac- ter in a command sent to the shell. If LESS- METAESCAPE is an empty string, commands containing metacharacters will not be passed to the shell. LESSOPEN Command line to invoke the (optional) input-prepro- cessor. LESSSECURE Runs less in "secure" mode. See discussion under SECURITY. LESSSEPARATOR String to be appended to a directory name in file- name completion. LINES Sets the number of lines on the screen. Takes precedence over the number of lines specified by the TERM variable. (But if you have a windowing system which supports TIOCGWINSZ or WIOCGETD, the window system's idea of the screen size takes precedence over the LINES and COLUMNS environment variables.) PATH User's search path (used to find a lesskey file on MS-DOS and OS/2 systems). SHELL The shell used to execute the ! command, as well as Version 335: 03 Apr 1999 25 LESS(1) LESS(1) 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 dis- abled 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. (This problem does not occur when less is compiled to use the POSIX regular expression package.) On some systems, setlocale claims that ASCII characters 0 thru 31 are control characters rather than binary charac- ters. 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) 1984,1985,1989,1994,1995,1996,1999 Mark Nudelman Comments to: marknu@flash.net Version 335: 03 Apr 1999 26
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