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LESS(1) LESS(1) NAME less - opposite of more SYNOPSIS less -? less [-[+]aBcCdeEfHimMnNqQrsSuUw] [-b bufs] [-h lines] [-j line] [-k keyfile] [-{oO} logfile] [-p pattern] [-P prompt] [-t tag] [-T tagfile] [-x tab] [-y lines] [-[z] lines] [+[+]cmd] [filename]... DESCRIPTION Less is a program similar to more (1), but which allows backward movement in the file as well as forward movement. Also, less does not have to read the entire input file before starting, so with large input files it starts up faster than text editors like vi (1). Less uses termcap (or terminfo on some systems), so it can run on a variety of terminals. There is even limited support for hardcopy terminals. (On a hardcopy terminal, lines which should be printed at the top of the screen are prefixed with an up- arrow.) 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. 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. 1 LESS(1) LESS(1) 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. 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 2 LESS(1) LESS(1) 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. (This works if standard input is being read, but only if less has already read to the end of the file. It is always fast, but not always useful.) { 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 3 LESS(1) LESS(1) 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 con- taining 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: ! Search for lines which do NOT match the pat- tern. * 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. @ 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. ?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: 4 LESS(1) LESS(1) ! Search for lines which do NOT match the pat- tern. * 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. @ 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. 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 !, the search is made for the N-th line NOT containing the pattern. If the previous search was modified by *, the search continues in the next (or previous) file if not satisfied in the current file. There is no effect if the previous search was modified by @. 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 *. ESC-N Repeat previous search, but in the reverse direc- tion and crossing file boundaries. :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 5 LESS(1) LESS(1) previously examined file. The filename is inserted into the command line list of files so that it can be seen by subsequent :n and :p commands. If the filename consists of several files, they are all inserted into the list of files and the first one is examined. ^X^V or E Same as :e. Warning: some systems use ^V as a spe- cial literalization character. :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 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. 6 LESS(1) LESS(1) -- 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 ZZ or ESC ESC Exits less. The following three 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 EDITOR, or defaults to "vi". 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. In all cases, the shell is taken from the environment variable SHELL, or defaults to "sh". | <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 7 LESS(1) LESS(1) 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. OPTIONS Command line options are described below. Most options may be changed while less is running, via the "-" command. Options are also taken from the environment variable "LESS". For example, to avoid typing "less -options ..." each time less is invoked, you might tell csh: setenv LESS "-options" or if you use sh: LESS="-options"; export LESS The environment variable is parsed before the command line, so command line options override the LESS 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 "-+". A dollar sign ($) may be used to signal the end of an option string. This is important only for options like -P which take a following string. -? This option displays a summary of the commands accepted by less (the same as the h command). If this option is given, all other options are ignored, and less exits after the help screen is viewed. (Depending on how your shell interprets the question mark, it may be necessary to quote the question mark, thus: "-\?".) -a Causes searches to start after the last line 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 Causes less to use a non-standard number of buffers. Buffers are 1K, and by default 10 buffers are used (except if data in coming from standard input; see the -B option). The number n specifies a different number of buffers to use. -B Disables automatic allocation of buffers, so that only the default number of buffers are used. If more data is read than will fit in the buffers, the oldest data is discarded. By default, when data is coming from standard input, buffers are allocated 8 LESS(1) LESS(1) automatically as needed to avoid loss of data. -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). -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. -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. Also, text which is overstruck or underlined can be searched for. This option is ignored if any uppercase let- ters appear in the search pattern. -jn Specifies a line on the screen where "target" lines are to be positioned. Target lines are the object of text searches, tag searches, jumps to a line number, jumps to a file percentage, and jumps 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 immedi- ately after the target line. For example, if "-j4" 9 LESS(1) LESS(1) 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 a file called .less exists in the user's home directory, this file 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 flag 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 specifying +/pattern; that is, it tells less to start at the first occurence of pattern in the file. 10 LESS(1) LESS(1) -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. -P followed by a string changes the default (short) prompt to that string. -Pm changes the medium (-m) prompt to the string, and -PM changes the long (-M) prompt. Also, -P= changes the message printed by the = command to the given string. All prompt strings consist of a sequence of letters and spe- cial 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 flag 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 charac- ter). 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 11 LESS(1) LESS(1) 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 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. -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. -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, as in "-n" for com- patibility with more. + 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 12 LESS(1) LESS(1) 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. KEY BINDINGS You may define your own less commands by using the program lesskey (1) to create a file called ".less" in your home directory. This file specifies a set of command keys and an action associated with each key. See the lesskey man- ual page for more details. NATIONAL CHARACTER SETS There are three types of characters in the input file: normal characters can be displayed directly to the screen. control characters should not be displayed directly, but are expected to be found in ordinary text files (such as backspace and tab). binary characters cannot be displayed directly and are not expected to be found in text files. By default, less uses the ASCII character set. In the ASCII character set, characters with values between 128 and 255 are treated as binary. The LESSCHARSET environ- ment variable may be used to select another character set. If it is set to the value "latin1", the ISO 8859/1 charac- ter set is assumed. Latin-1 is the same as ASCII, except characters between 128 and 255 are treated as normal char- acters. The only valid values for LESSCHARSET currently are "ascii" and "latin1". 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 13 LESS(1) LESS(1) would be normal. (This is an example, and does not neces- sarily represent any real character set.) Setting LESSCHARDEF to "8bcccbcc18b95.b" is the same as setting LESSCHARSET to "ascii". Setting LESSCHARDEF to "8bcccbcc18b95.33b." is the same as setting LESSCHARSET to "latin1". Control and binary characters are displayed in blinking mode. 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 dis- played as an octal number preceded by a backslash. This octal format can be changed by setting the LESSBINFMT environment variable to a printf-style format string; the default is '\%o'. The blinking mode display of control and binary characters can be changed or disabled by pre- ceding the LESSBINFMT format string with a "*" and one character to select the mode: "*k" is blinking, "*d" is bold, "*u" is underlined, and "*n" is normal (no special display attribute). For example, if LESSBINFMT is "*u[%x]", binary characters are displayed in underlined hexadecimal surrounded by brackets. 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. %E Replaced by the name of the editor (from the EDITOR environment variable). See the discussion of the LESSEDIT feature below. 14 LESS(1) LESS(1) %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. 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. 15 LESS(1) LESS(1) ?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 file- name 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 refer- ence, here are the defaults for the other two prompts (-m and -M respectively). Each is broken into two lines here 16 LESS(1) LESS(1) 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. ENVIRONMENT VARIABLES 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 .less file). LESS Flags 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. LESSEDIT Editor prototype string (used for the v command). 17 LESS(1) LESS(1) See discussion under PROMPTS. LESSHELP Name of the help file. LINES Sets the number of lines on the screen. Takes precedence over the number of lines specified by the TERM variable. 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. REGULAR EXPRESSION SYNTAX This segment is extracted from regexp.3 in Henry Spencer's regexp package. The entire regexp package can be obtained separately. A regular expression is zero or more branches, separated by `|'. It matches anything that matches one of the branches. A branch is zero or more pieces, concatenated. It matches a match for the first, followed by a match for the second, etc. A piece is an atom possibly followed by `*', `+', or `?'. An atom followed by `*' matches a sequence of 0 or more matches of the atom. An atom followed by `+' matches a sequence of 1 or more matches of the atom. An atom fol- lowed by `?' matches a match of the atom, or the null string. An atom is a regular expression in parentheses (matching a match for the regular expression), a range (see below), `.' (matching any single character), `^' (matching the null string at the beginning of the input string), `$' (matching the null string at the end of the input string), a `\' followed by a single character (matching that char- acter), or a single character with no other significance (matching that character). A range is a sequence of characters enclosed in `[]'. It normally matches any single character from the sequence. If the sequence begins with `^', it matches any single character not from the rest of the sequence. If two char- acters in the sequence are separated by `-', this is shorthand for the full list of ASCII characters between them (e.g. `[0-9]' matches any decimal digit). To include a literal `]' in the sequence, make it the first character (following a possible `^'). To include a literal `-', make it the first or last character. 18 LESS(1) LESS(1) AMBIGUITY If a regular expression could match two different parts of the input string, it will match the one which begins ear- liest. If both begin in the same place but match different lengths, or match the same length in different ways, life gets messier, as follows. In general, the possibilities in a list of branches are considered in left-to-right order, the possibilities for `*', `+', and `?' are considered longest-first, nested constructs are considered from the outermost in, and con- catenated constructs are considered leftmost-first. The match that will be chosen is the one that uses the earli- est possibility in the first choice that has to be made. If there is more than one choice, the next will be made in the same manner (earliest possibility) subject to the decision on the first choice. And so forth. For example, `(ab|a)b*c' could match `abc' in one of two ways. The first choice is between `ab' and `a'; since `ab' is earlier, and does lead to a successful overall match, it is chosen. Since the `b' is already spoken for, the `b*' must match its last possibility--the empty string--since it must respect the earlier choice. In the particular case where no `|'s are present and there is only one `*', `+', or `?', the net effect is that the longest possible match will be chosen. So `ab*', pre- sented with `xabbbby', will match `abbbb'. Note that if `ab*' is tried against `xabyabbbz', it will match `ab' just after `x', due to the begins-earliest rule. (In effect, the decision on where to start the match is the first choice to be made, hence subsequent choices must respect it even if this leads them to less-preferred alternatives.) 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. The handling of national character sets is nonstandard as well as insufficient for multibyte characters. It will probably change in a later release. 19