每天一个linux命令(13):less命令

1、命令简介

less(less)  命令可以对文件或其它输出进行分页显示，与moe命令相似，但是比more命令要强大许多。应该说是linux正统查看文件内容的工具。

2、用法

less  [选项]... [文件]...

3、选项

---------------------------------------------------------------------------

                           OPTIONS

        Most options may be changed either on the command line,
        or from within less by using the - or -- command.
        Options may be given in one of two forms: either a single
        character preceded by a -, or a name preceeded by --.

  -?  ........  --help   显示帮助
  -a  ........  --search-skip-screen
                  Forward search skips current screen.
  -b [N]  ....  --buffers=[N]
                  Number of buffers.  设置缓冲区的大小
  -B  ........  --auto-buffers
                  Don't automatically allocate buffers for pipes.
  -c  -C  ....  --clear-screen --CLEAR-SCREEN
                  Repaint by clearing rather than scrolling.  先清除屏幕后再显示内容

  -d  ........  --dumb
                  Dumb terminal.
  -D [xn.n]  .  --color=xn.n
                  Set screen colors. (MS-DOS only)
  -e  -E  ....  --quit-at-eof  --QUIT-AT-EOF
                  Quit at end of file.  当文件显示结束后，自动离开
  -f  ........  --force
                  Force open non-regular files.强迫打开特殊文件，例如外围设备代号、目录和二进制文件
  -F  ........  --quit-if-one-screen
                  Quit if entire file fits on first screen.
  -g  ........  --hilite-search
                  Highlight only last match for searches.不加亮显示搜索到的所有关键词，仅显示当前显示的关键字，以提高显示速度；
  -G  ........  --HILITE-SEARCH
                  Don't highlight any matches for searches.
  -h [N]  ....  --max-back-scroll=[N]
                  Backward scroll limit.
  -i  ........  --ignore-case
                  Ignore case in searches that do not contain uppercase. 忽略搜索时的大小写
  -I  ........  --IGNORE-CASE
                  Ignore case in all searches.
  -j [N]  ....  --jump-target=[N]
                  Screen position of target lines.
  -J  ........  --status-column
                  Display a status column at left edge of screen.
  -k [file]  .  --lesskey-file=[file]
                  Use a lesskey file.
  -L  ........  --no-lessopen
                  Ignore the LESSOPEN environment variable.
  -m  -M  ....  --long-prompt  --LONG-PROMPT
                  Set prompt style.  显示类似more命令的百分比
  -n  ........  --line-numbers
                  Don't use line numbers.
  -N  ........  --LINE-NUMBERS
                  Use line numbers.   显示每行的行号
  -o [file]  .  --log-file=[file]
                  Copy to log file (standard input only). 将less 输出的内容在指定文件中保存起来
  -O [file]  .  --LOG-FILE=[file]
                  Copy to log file (unconditionally overwrite).
  -p [pattern]  --pattern=[pattern]
                  Start at pattern (from command line).
  -P [prompt]   --prompt=[prompt]
                  Define new prompt.
  -q  -Q  ....  --quiet  --QUIET  --silent --SILENT
                  Quiet the terminal bell.
  -r  -R  ....  --raw-control-chars  --RAW-CONTROL-CHARS
                  Output "raw" control characters.
  -s  ........  --squeeze-blank-lines
                  Squeeze multiple blank lines. 显示连续空行为一行
  -S  ........  --chop-long-lines
                  Chop long lines.
  -t [tag]  ..  --tag=[tag]
                  Find a tag.
  -T [tagsfile] --tag-file=[tagsfile]
                  Use an alternate tags file.
  -u  -U  ....  --underline-special  --UNDERLINE-SPECIAL
                  Change handling of backspaces.
  -V  ........  --version
                  Display the version number of "less".
  -w  ........  --hilite-unread
                  Highlight first new line after forward-screen.
  -W  ........  --HILITE-UNREAD
                  Highlight first new line after any forward movement.
  -x [N[,...]]  --tabs=[N[,...]]
                  Set tab stops.
  -X  ........  --no-init
                  Don't use termcap init/deinit strings.
                --no-keypad
                  Don't use termcap keypad init/deinit strings.
  -y [N]  ....  --max-forw-scroll=[N]
                  Forward scroll limit.
  -z [N]  ....  --window=[N]
                  Set size of window.
  -" [c[c]]  .  --quotes=[c[c]]
                  Set shell quote characters.
  -~  ........  --tilde
                  Don't display tildes after end of file.
  -# [N]  ....  --shift=[N]
                  Horizontal scroll amount (0 = one half screen width)

 ---------------------------------------------------------------------------

4、支持的操作

1、MOVING

---------------------------------------------------------------------------

                           MOVING

  e  ^E  j  ^N  CR  *  Forward  one line   (or N lines). 下移一行
  y  ^Y  k  ^K  ^P  *  Backward one line   (or N lines). 上移一行
  f  ^F  ^V  SPACE  *  Forward  one window (or N lines). 下移一屏
  b  ^B  ESC-v      *  Backward one window (or N lines).  回退一屏
  z                 *  Forward  one window (and set window to N).下移一屏
  w                 *  Backward one window (and set window to N).回退一屏  

  ESC-SPACE         *  Forward  one window, but don't stop at end-of-file.下移一屏
  d  ^D             *  Forward  one half-window (and set half-window to N). 下移半屏
  u  ^U             *  Backward one half-window (and set half-window to N).  回退半屏
  ESC-)  RightArrow *  Left  one half screen width (or N positions).
  ESC-(  LeftArrow  *  Right one half screen width (or N positions).
  F                    Forward forever; like "tail -f".
  r  ^R  ^L            Repaint screen.
  R                    Repaint screen, discarding buffered input.
        ---------------------------------------------------
        Default "window" is the screen height.
        Default "half-window" is half of the screen height.
 ---------------------------------------------------------------------------

2 SEARCHING

---------------------------------------------------------------------------

                          SEARCHING

  /pattern          *  Search forward for (N-th) matching line. 使用一个模式进行搜索，并定位到下一个匹配的文本
  ?pattern          *  Search backward for (N-th) matching line. ? ： 使用模式进行搜索，并定位到前一个匹配的文本

  n                 *  Repeat previous search (for N-th occurrence).查找下一个匹配的文本
  N                 *  Repeat previous search in reverse direction. 查找上一个匹配的文本
  ESC-n             *  Repeat previous search, spanning files.
  ESC-N             *  Repeat previous search, reverse dir. & spanning files.
  ESC-u                Undo (toggle) search highlighting.
  &pattern          *  Display only matching lines
        ---------------------------------------------------
        Search patterns may be modified by one or more of:
        ^N or !  Search for NON-matching lines.
        ^E or *  Search multiple files (pass thru END OF FILE).
        ^F or @  Start search at FIRST file (for /) or last file (for ?).
        ^K       Highlight matches, but don't move (KEEP position).
        ^R       Don't use REGULAR EXPRESSIONS.
 ---------------------------------------------------------------------------

3、JUMPING

---------------------------------------------------------------------------

                           JUMPING

  g  < ESC-<        * Go to first line in file (or line N). 跳到第一行 

  G >  ESC->        *  Go to last line in file (or line N).  调到最后一行
  p  %              *  Go to beginning of file (or N percent into file).
  t                 *  Go to the (N-th) next tag.
  T                 *  Go to the (N-th) previous tag.
  {  (  [           *  Find close bracket } ) ].
  }  )  ]           *  Find open bracket { ( [.
  ESC-^F <c1> <c2>  *  Find close bracket <c2>.
  ESC-^B <c1> <c2>  *  Find open bracket <c1>
        ---------------------------------------------------
        Each "find close bracket" command goes forward to the close bracket
          matching the (N-th) open bracket in the top line.
        Each "find open bracket" command goes backward to the open bracket
          matching the (N-th) close bracket in the bottom line.

  m<letter>            Mark the current position with <letter>.
  '<letter>            Go to a previously marked position.
  ''                   Go to the previous position.
  ^X^X                 Same as '.
        ---------------------------------------------------
        A mark is any upper-case or lower-case letter.
        Certain marks are predefined:
             ^  means  beginning of the file
             $  means  end of the file
 ---------------------------------------------------------------------------

4、CHANGING FILES

---------------------------------------------------------------------------

                        CHANGING FILES

  :e [file]            Examine a new file.进入编辑模式，使用配置的编辑器编辑当前文件
  ^X^V                 Same as :e.
  :n                *  Examine the (N-th) next file from the command line. 浏览下一个文件
  :p                *  Examine the (N-th) previous file from the command line. 浏览前一个文件
  :x                *  Examine the first (or N-th) file from the command line.
  :d                   Delete the current file from the command line list.
  =  ^G  :f            Print current file name.
 ---------------------------------------------------------------------------

5、MISCELLANEOUS COMMANDS

---------------------------------------------------------------------------

                    MISCELLANEOUS COMMANDS

  -<flag>              Toggle a command line option [see OPTIONS below].
  --<name>             Toggle a command line option, by name.
  _<flag>              Display the setting of a command line option.
  __<name>             Display the setting of an option, by name.
  +cmd                 Execute the less cmd each time a new file is examined.

  !command             Execute the shell command with $SHELL. 执行命令
  |Xcommand            Pipe file between current pos & mark X to shell command.
  v                    Edit the current file with $VISUAL or $EDITOR.
  V                    Print version number of "less".
 ---------------------------------------------------------------------------

6、LINE EDITING

---------------------------------------------------------------------------

                          LINE EDITING

        These keys can be used to edit text being entered
        on the "command line" at the bottom of the screen.

 RightArrow                       ESC-l     Move cursor right one character.
 LeftArrow                        ESC-h     Move cursor left one character.
 CNTL-RightArrow  ESC-RightArrow  ESC-w     Move cursor right one word.
 CNTL-LeftArrow   ESC-LeftArrow   ESC-b     Move cursor left one word.
 HOME                             ESC-0     Move cursor to start of line.
 END                              ESC-$     Move cursor to end of line.
 BACKSPACE                                  Delete char to left of cursor.
 DELETE                           ESC-x     Delete char under cursor.
 CNTL-BACKSPACE   ESC-BACKSPACE             Delete word to left of cursor.
 CNTL-DELETE      ESC-DELETE      ESC-X     Delete word under cursor.
 CNTL-U           ESC (MS-DOS only)         Delete entire line.
 UpArrow                          ESC-k     Retrieve previous command line.
 DownArrow                        ESC-j     Retrieve next command line.
 TAB                                        Complete filename & cycle.
 SHIFT-TAB                        ESC-TAB   Complete filename & reverse cycle.
 CNTL-L                                     Complete filename, list all.
---------------------------------------------------------------------------

5、示例

1、查看文件

[root@oracledb log]# less  boot.log

2、查看命令历史使用记录并通过less分页显示

[root@oracledb ~]# history|less

    1  yum update
    2  vi /etc/sysconfig/network
    3  vi /etc/sysconfig/network-scripts/ifcfg-eth0
    4  service network restart
    5  ipconfig
    6  ifconfig
    7  clear
    8  yum update
    9  clear
   10  yum update

3、less -s file 逐页显示 testfile 之档案内容，如有连续两行以上空白行则以一行空白行显示。

[root@oracledb study]# less 

 -s test.log
2016
2017

2018前面有两空行

4、less进行中执行命令!ifconfig

[root@oracledb ~]# history|less
eth5      Link encap:Ethernet  HWaddr 08:00:27:60:11:C4
          inet addr:172.17.22.31  Bcast:172.17.23.255  Mask:255.255.254.0
          inet6 addr: fe80::a00:27ff:fe60:11c4/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:61468 errors:0 dropped:0 overruns:0 frame:0
          TX packets:23800 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:67329469 (64.2 MiB)  TX bytes:1645628 (1.5 MiB)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:16 errors:0 dropped:0 overruns:0 frame:0
          TX packets:16 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:1584 (1.5 KiB)  TX bytes:1584 (1.5 KiB)

!done  (press RETURN)

5、根据模式查找字符串，输入斜杠 /模式字符串 回车进行查找，n和N控制向上和向下查找

# Mandatory: no
# Range: 60-3600
# 上面为more的显示内容

/Hostname=Zabbix server

查找出的结果在最上面显示

...skipping
# Hostname=

Hostname=Zabbix server

### Option: HostnameItem
#    Item used for generating Hostname if it is undefined. Ignored if Hostname is defined.
#    Does not support UserParameters or aliases.

6：浏览多个文件

正在浏览一个文件时，使用 :e 打开另一个文件。

[root@zabbix zabbix]# less zabbix_server.log

30473:20160419:202118.691 active check configuration update from [127.0.0.1:10051] started to fail (cannot connect to [[127.0.0.1]:10051]: [111] Connection refused)
 30473:20160419:223818.547 active check configuration update from [127.0.0.1:10051] is working again
 30473:20160423:152419.606 active check configuration update from [127.0.0.1:10051] started to fail (cannot connect to [[127.0.0.1]:10051]: [111] Connection refused)
 30473:20160423:153119.727 active check configuration update from [127.0.0.1:10051] is working again
Examine: zabbix_agentd.log

7:  浏览多个文件

[root@zabbix zabbix]# less zabbix_server.log zabbix_agentd.log
 20911:20160417:041935.968 slow query: 3.220461 sec, "commit;"
 20913:20160417:041935.982 slow query: 3.092948 sec, "commit;"

zabbix_server.log (file 1 of 2)

输入:n后，切换到zabbix_agentd.log

[root@zabbix zabbix]# less zabbix_server.log zabbix_agentd.log 

30473:20160419:223818.547 active check configuration update from [127.0.0.1:10051] is working again
30473:20160423:153119.727 active check configuration update from [127.0.0.1:10051] is working again

zabbix_agentd.log (

file 2 of 2) (END)

输入:p 后，切换到zabbix_server.log

8 less 版 tail –f  动态查看日志文件

使用 less file-name 打开日志文件，按 F 可以实现类似 tail -f 的效果。按ctrl+c退出。

[root@oracledb ~]# 

less

  log.txt

按F，出现 Waiting for data... (interrupt to abort)

2014
2015
2016
2017
Waiting 

for data... (interrupt to abort)

在另一个窗口更改文件内容

[root@oracledb ~]# echo "2018" >> log.txt

less 动态输出新增的内容

2014
2015
2016
2017
2018
Waiting for data... (interrupt to abort)

ctrl+c 退出

2014
2015
2016
2017
2018
Line numbers turned off  (press RETURN)