linux command


Linux Command – less ใช้ในการอ่านข้อมูลและค้นหาข้อมูลใน file



1. เปิดอ่าน file

$ less sample.txt

Line 1
Hi i am a good boy.
I am x . 
Be cool and calm 
Happy birthday 
I am  Bond 00 7 
Eurekaa !!! I Got it !
Yesssssssssssssss yes 
sample.txt (END)

ออกจาก prompt ด้วยการกด q


2. เปิดอ่าน file โดย clear screen ก่อน เพื่อให้เหลือแต่ content

$ less -c sample.txt


3. ใช้ดู ouput ขนาดใหญ่

$ ls -la |less
total 38644
drwxr-xr-x 2 root root 69632 May 8 17:04 .
drwxr-xr-x 7 root root 4096 Apr 20 17:08 ..
-rw-r--r-- 1 root root 13950 May 8 17:29 controller.log
-rw-r--r-- 1 root root 17959 Apr 5 03:59 controller.log.2017-04-05-03
-rw-r--r-- 1 root root 6360 Apr 5 04:59 controller.log.2017-04-05-04
-rw-r--r-- 1 root root 6360 Apr 5 05:59 controller.log.2017-04-05-05
-rw-r--r-- 1 root root 6360 Apr 5 06:59 controller.log.2017-04-05-06
-rw-r--r-- 1 root root 6360 Apr 5 07:59 controller.log.2017-04-05-07


4. การค้นหาข้อมูลใน file

การย้าย cursor

 *   [Arrows]/[Page Up]/[Page Down]/[Home]/[End]: Navigation.
 *   [Space bar]: Next page.
 *   b: Previous page.
 *   ng: Jump to line number n. Default is the start of the file.
 *   nG: Jump to line number n. Default is the end of the file.
 *   /pattern: Search for pattern. Regular expressions can be used.
 *   n: Go to next match (after a successful search).
 *   N: Go to previous match.
 *   ‘^ or g: Go to start of file.
 *   ‘$ or G: Go to end of file.
 *   s: Save current content (got from another program like grep) in a file.
 *   =: File information.
 *   F: continually read information from file and follow its end. Useful for logs watching. Use Ctrl+C to exit this mode.
 *   -option: Toggle command-line option -option.
 *   h: Help.
 *   q or zz: Quit.



  *  / – search for a pattern which will take you to the next occurrence.
  *  n – for next match in forward
  *  N – for previous match in backward



  *  ? – search for a pattern which will take you to the previous occurrence.
  *  n – for next match in forward
  *  N – for previous match in backward



  *  j – navigate forward by one line
  *  k – navigate backward by one line



  *  CTRL+D – forward half window
  *  CTRL+U – backward half window
  *  CTRL+F – forward one window
  *  CTRL+B – backward one window



  *  5j – 5 lines forward.
  *  10k – 10 lines backward.


Option พิเศษ

  *  :p - Examine the previous file in the command line list.
  *  :d - Remove the current file from the list of files.
  *  v – using the configured editor edit the current file.
  *  &pattern – display only the matching lines, not all.
  *  CTRL+G – show the current file name along with line, byte and percentage statistics.
  *  mx – mark the current position with the letter ‘x’.
  *  ‘x – go to the marked position ‘x’.



 less -?
 less --help
 less -V
 less --version
 less [-[+]aABcCdeEfFgGiIJKLmMnNqQrRsSuUVwWX~]
      [-b space] [-h lines] [-j line] [-k keyfile]
      [-{oO} logfile] [-p pattern] [-P prompt] [-t tag]
      [-T tagsfile] [-x tab,...] [-y lines] [-[z] lines]
      [-# shift] [+[+]cmd] [--] [filename]...



เป็นคำสั่งที่ใช้ในการอ่านข้อมูลและค้นหาข้อมูลใน file ทำงานคล้ายๆกับคำสั่ง “more”



 -? or --help
 This option displays a summary of the commands accepted by less (the same as the h command). (Depending on how your shell interprets the question mark, it may be necessary
 to quote the question mark, thus: "-\?".)

 -a or --search-skip-screen
 By default, forward searches start at the top of the displayed screen and backwards searches start at the bottom of the displayed screen (except for repeated searches
 invoked by the n or N commands, which start after or before the "target" line respectively; see the -j option for more about the target line). The -a option causes forward
 searches to instead start at the bottom of the screen and backward searches to start at the top of the screen, thus skipping all lines displayed on the screen.

 Causes all forward searches (not just non-repeated searches) to start just after the target line, and all backward searches to start just before the target line. Thus, for‐
 ward searches will skip part of the displayed screen (from the first line up to and including the target line). Similarly backwards searches will skip the displayed screen
 from the last line up to and including the target line. This was the default behavior in less versions prior to 441.

 -bn or --buffers=n
 Specifies the amount of buffer space less will use for each file, in units of kilobytes (1024 bytes). By default 64 K of buffer space is used for each file (unless the file
 is a pipe; see the -B option). The -b option specifies instead that n kilobytes of buffer space should be used for each file. If n is -1, buffer space is unlimited; that
 is, the entire file can be read into memory.

 -B or --auto-buffers
 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 64 K (or the amount of space specified by the -b option) is used
 for the pipe. Warning: use of -B can result in erroneous display, since only the most recently viewed part of the piped data is kept in memory; any earlier data is lost.

 -c or --clear-screen
 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.

 Same as -c, for compatibility with older versions of less.

 -d or --dumb
 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 or --color=xcolor
 [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=under‐
 lined, 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.M, where M is the normal background color.

 -e or --quit-at-eof
 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 or --QUIT-AT-EOF
 Causes less to automatically exit the first time it reaches end-of-file.

 -f or --force
 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. Note that some operating systems will not allow directories to be read, even if -f is set.

 -F or --quit-if-one-screen
 Causes less to automatically exit if the entire file can be displayed on the first screen.

 -g or --hilite-search
 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.

 The -G option suppresses all highlighting of strings found by search commands.

 -hn or --max-back-scroll=n
 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 or --ignore-case
 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.

 Like -i, but searches ignore case even if the pattern contains uppercase letters.

 -jn or --jump-target=n
 Specifies a line on the screen where the "target" line is to be positioned. The target line is the line specified by any command to search for a pattern, jump to a line
 number, jump to a file percentage or jump to a tag. The screen line may be 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. Alternately, the screen
 line may be specified as a fraction of the height of the screen, starting with a decimal point: .5 is in the middle of the screen, .3 is three tenths down from the first
 line, and so on. If the line is specified as a fraction, the actual line number is recalculated if the terminal window is resized, so that the target line remains at the
 specified fraction of the screen height. If any form of the -j option is used, repeated forward searches (invoked with "n" or "N") begin at the line immediately after the
 target line, and repeated backward searches begin at the target line, unless changed by -a or -A. For example, if "-j4" is used, the target line is the fourth line on the
 screen, so forward searches begin at the fifth line on the screen. However nonrepeated searches (invoked with "/" or "?") always begin at the start or end of the current
 screen respectively.

 -J or --status-column
 Displays a status column at the left edge of the screen. The status column shows the lines that matched the current search. The status column is also used if the -w or -W
 option is in effect.

 -kfilename or --lesskey-file=filename
 Causes less to open and interpret the named file as a lesskey (1) file. Multiple -k options may be specified. If the LESSKEY or LESSKEY_SYSTEM 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.

 -K or --quit-on-intr
 Causes less to exit immediately (with status 2) when an interrupt character (usually ^C) is typed. Normally, an interrupt character causes less to stop whatever it is doing
 and return to its command prompt. Note that use of this option makes it impossible to return to the command prompt from the "F" command.

 -L or --no-lessopen
 Ignore the LESSOPEN environment variable (see the INPUT PREPROCESSOR section below). This option can be set from within less, but it will apply only to files opened subse‐
 quently, not to the file which is currently open.

 -m or --long-prompt
 Causes less to prompt verbosely (like more), with the percent into the file. By default, less prompts with a colon.

 Causes less to prompt even more verbosely than more.

 -n or --line-numbers
 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 num‐
 bers 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).

 Causes a line number to be displayed at the beginning of each line in the display.

 -ofilename or --log-file=filename
 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 or --LOG-FILE=filename
 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 or --pattern=pattern
 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 or --prompt=prompt
 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.
 -Pw changes the message printed while waiting for data (in the F command). All prompt strings consist of a sequence of letters and special escape sequences. See the sec‐
 tion on PROMPTS for more details.

 -q or --quiet or --silent
 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 ter‐
 minal 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 or --QUIET or --SILENT
 Causes totally "quiet" operation: the terminal bell is never rung.

 -r or --raw-control-chars
 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 con‐
 trol character). Thus, various display problems may result, such as long lines being split in the wrong place.

 Like -r, but only ANSI "color" escape sequences are output in "raw" form. Unlike -r, the screen appearance is maintained correctly in most cases. ANSI "color" escape
 sequences are sequences of the form:

 ESC [ ... m

 where the "..." is zero or more color specification characters For the purpose of keeping track of screen appearance, ANSI color escape sequences are assumed to not move the
 cursor. You can make less think that characters other than "m" can end ANSI color escape sequences by setting the environment variable LESSANSIENDCHARS to the list of char‐
 acters which can end a color escape sequence. And you can make less think that characters other than the standard ones may appear between the ESC and the m by setting the
 environment variable LESSANSIMIDCHARS to the list of characters which can appear.

 -s or --squeeze-blank-lines
 Causes consecutive blank lines to be squeezed into a single blank line. This is useful when viewing nroff output.

 -S or --chop-long-lines
 Causes lines longer than the screen width to be chopped (truncated) rather than wrapped. That is, the portion of a long line that does not fit in the screen width is not
 shown. The default is to wrap long lines; that is, display the remainder on the next line.

 -ttag or --tag=tag
 The -t option, followed immediately by a TAG, will edit the file containing that tag. For this to work, tag information must be available; for example, there may be a file
 in the current directory called "tags", which was previously built by ctags (1) or an equivalent command. If the environment variable LESSGLOBALTAGS is set, it is taken to
 be the name of a command compatible with global (1), and that command is executed to find the tag. (See The -t 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 or --tag-file=tagsfile
 Specifies a tags file to be used instead of "tags".

 -u or --underline-special
 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.

 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 ter‐
 minal's hardware underlining capability. Also, backspaces which appear between two identical characters are treated specially: the overstruck text is printed using the ter‐
 minal'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 or --version
 Displays the version number of less.

 -w or --hilite-unread
 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 bot‐
 tom of the screen. Also highlights the target line after a g or p command. The highlight is removed at the next command which causes movement. The entire line is high‐
 lighted, unless the -J option is in effect, in which case only the status column is highlighted.

 Like -w, but temporarily highlights the first new line after any forward movement command larger than one line.

 -xn,... or --tabs=n,...
 Sets tab stops. If only one n is specified, tab stops are set at multiples of n. If multiple values separated by commas are specified, tab stops are set at those posi‐
 tions, and then continue with the same spacing as the last two. For example, -x9,17 will set tabs at positions 9, 17, 25, 33, etc. The default for n is 8.

 -X or --no-init
 Disables sending the termcap initialization and deinitialization strings to the terminal. This is sometimes desirable if the deinitialization string does something unneces‐
 sary, like clearing the screen.

 -yn or --max-forw-scroll=n
 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 or --window=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 omit‐
 ted for compatibility with some versions of 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.

 -"cc or --quotes=cc
 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 char‐
 acter, 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

 -~ or --tilde
 Normally lines after end of file are displayed as a single tilde (~). This option causes lines after end of file to be displayed as blank lines.

 -# or --shift
 Specifies the default number of positions to scroll horizontally in the RIGHTARROW and LEFTARROW commands. If the number specified is zero, it sets the default number of
 positions to one half of the screen width. Alternately, the number may be specified as a fraction of the width of the screen, starting with a decimal point: .5 is half of
 the screen width, .3 is three tenths of the screen width, and so on. If the number is specified as a fraction, the actual number of scroll positions is recalculated if the
 terminal window is resized, so that the actual scroll remains at the specified fraction of the screen width.

 Normally, if the input file is renamed while an F command is executing, less will continue to display the contents of the original file despite its name change. If --fol‐
 low-name is specified, during an F command less will periodically attempt to reopen the file by name. If the reopen succeeds and the file is a different file from the orig‐
 inal (which means that a new file has been created with the same name as the original (now renamed) file), less will display the contents of that new file.

 Disables sending the keypad initialization and deinitialization strings to the terminal. This is sometimes useful if the keypad strings make the numeric keypad behave in an
 undesirable manner.

 This option changes the interpretations of options which follow this one. After the --use-backslash option, any backslash in an option string is removed and the following
 character is taken literally. This allows a dollar sign to be included in option strings.

 -- 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.






คำสั่ง Unix – Linux Command

Linux, Unix


Author: Suphakit Annoppornchai


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