SUMMARY OF LESS COMMANDS

November 18, 2019 in Learning, Tips and Tricks

SUMMARY OF LESS COMMANDS

Less command is linux utility which can be used to read contents of text file one page(one screen) per time. It has faster access because if file is large, it don’t access complete file, but access it page by page.

For example, if it’s a large file and you are reading it using any text editor, then the complete file will be loaded to main memory, but less command don’t load entire file, but load it part by part, which makes it faster.

      Commands marked with * may be preceded by a number, N.
      Notes in parentheses indicate the behavior if N is given.
      A key preceded by a caret indicates the Ctrl key; thus ^K is ctrl-K.

  h  H                 Display this help.
  q  :q  Q  :Q  ZZ     Exit.
 ---------------------------------------------------------------------------

                           MOVING

  e  ^E  j  ^N  CR  *  Forward  one line   (or N lines).
  y  ^Y  k  ^K  ^P  *  Backward one line   (or N lines).
  f  ^F  ^V  SPACE  *  Forward  one window (or N lines).
  b  ^B  ESC-v      *  Backward one window (or N lines).
  z                 *  Forward  one window (and set window to N).
  w                 *  Backward one window (and set window to N).
  ESC-SPACE         *  Forward  one window, but don't stop at end-of-file.
  d  ^D             *  Forward  one half-window (and set half-window to N).
  u  ^U             *  Backward one half-window (and set half-window to N).
  ESC-)  RightArrow *  Right one half screen width (or N positions).
  ESC-(  LeftArrow  *  Left  one half screen width (or N positions).
  ESC-}  ^RightArrow   Right to last column displayed.
  ESC-{  ^LeftArrow    Left  to first column.
  F                    Forward forever; like "tail -f".
  ESC-F                Like F but stop when search pattern is found.
  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.
 ---------------------------------------------------------------------------

                          SEARCHING

  /pattern          *  Search forward for (N-th) matching line.
  ?pattern          *  Search backward for (N-th) matching line.
  n                 *  Repeat previous search (for N-th occurrence).
  N                 *  Repeat previous search in reverse direction.
  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
        ---------------------------------------------------
        A search pattern may be preceded 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.
 ---------------------------------------------------------------------------

                           JUMPING

  g  <  ESC-<       *  Go to first line in file (or line N).
  G  >  ESC->       *  Go to last line in file (or line N).
  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
 ---------------------------------------------------------------------------

                        CHANGING FILES

  :e [file]            Examine a new file.
  ^X^V                 Same as :e.
  :n                *  Examine the (N-th) next file from the command line.
  :p                *  Examine the (N-th) previous file from the command line.
  :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.
 ---------------------------------------------------------------------------

                    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.
  |Xcommand            Pipe file between current pos & mark X to shell command.
  s file               Save input to a file.
  v                    Edit the current file with $VISUAL or $EDITOR.
  V                    Print version number of "less".
 ---------------------------------------------------------------------------

                           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 preceded by --.

  -?  ........  --help
                  Display help (from command line).
  -a  ........  --search-skip-screen
                  Search skips current screen.
  -A  ........  --SEARCH-SKIP-SCREEN
                  Search starts just after target line.
  -b [N]  ....  --buffers=[N]
                  Number of buffers.
  -B  ........  --auto-buffers
                  Don't automatically allocate buffers for pipes.
  -c  ........  --clear-screen
                  Repaint by clearing rather than scrolling.
  -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.
  -f  ........  --force
                  Force open non-regular files.
  -F  ........  --quit-if-one-screen
                  Quit if entire file fits on first screen.
  -g  ........  --hilite-search
                  Highlight only last match for searches.
  -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.
  -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.
  -K            --quit-on-intr
                  Exit less in response to ctrl-C.
  -L  ........  --no-lessopen
                  Ignore the LESSOPEN environment variable.
  -m  -M  ....  --long-prompt  --LONG-PROMPT
                  Set prompt style.
  -n  -N  ....  --line-numbers  --LINE-NUMBERS
                  Don't use line numbers.
  -o [file]  .  --log-file=[file]
                  Copy to log file (standard input only).
  -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.
  -S  ........  --chop-long-lines
                  Chop (truncate) long lines rather than wrapping.
  -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.
  -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)
      ........  --no-keypad
                  Don't send termcap keypad init/deinit strings.
      ........  --follow-name
                  The F command changes files if the input file is renamed.
      ........  --use-backslash
                  Subsequent options use backslash as escape char.


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

                          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.
 ctrl-RightArrow  ESC-RightArrow  ESC-w ... Move cursor right one word.
 ctrl-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.
 ctrl-BACKSPACE   ESC-BACKSPACE ........... Delete word to left of cursor.
 ctrl-DELETE .... ESC-DELETE .... ESC-X ... Delete word under cursor.
 ctrl-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.
 ctrl-L ................................... Complete filename, list all.

November 18, 2019 in Learning, Tips and Tricks

Unix Less Command: Tips for Effective Navigation

The navigation keys in less command are similar to Vim editor. In this article, let us look at few less command navigation and other operations which will make you a better command line warrior.

1. Less Command – Search Navigation

Once you’ve opened a log file (or any file) using less file-name, use the following keys to search. Please note that the match will be highlighted automatically by default.

Forward Search

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

Backward Search

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

Tip: If you dont bother about which direction the search is happening, and you want to search file path, or URL, such as “/home/ramesh/”, you can use backward search (?pattern) which will be handy as you don’t want to escape slashes each time.

Search Path
In forward: /\/home\/aditya\/
In backward: ?/home/aditya/

2. Less Command – Screen Navigation

Use the following screen navigation commands while viewing large log files.

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

3. Less Command – Line navigation

In a smaller chunk of data, where you want to locate particular error, you may want to navigate line by line using these keys:

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

4. Less Command – Other Navigations

The following are other navigation operations that you can use inside the less pager.

• G – go to the end of file
• g – go to the start of file
• q or ZZ – exit the less pager

5. Simulate tail -f inside less pager – Press F

Once you’ve opened a file using less command, any content that is appended to the file after that will not be displayed automatically. However, you can press F less command will show the status ‘waiting for data‘. This is as similar to ‘tail -f’.

6. Less Command – Count magic

Similar to Vim editor navigation command, you can give 10j to scroll 10 lines down, or 10k to go up by 10 lines.

• 10j – 10 lines forward.
• 10k – 10 lines backward.
• CTRL+G – show the current file name along with line, byte and percentage statistics.

7. Other useful Less Command Operations

• v – using the configured editor edit the current file.
• h – summary of less commands
• &pattern – display only the matching lines, not all.

8. Open any types of files using less command

less command can be used to open and view the following 10 different file types:

1. PDF File – *.pdf
2. Word Document- *.doc
3. Image Files – *.gif, *.jpg, *.jpeg, *.png
4. TAR Files – *.tar
5. TAR Files with gzip – *.tar.gz
6. Zip Files – *.zip
7. Gzip and Gzip2 Files – *.gz and *.bz2
8. ISO Files
9. Debian Files – *.deb
10. RPM Files – *.rpm

Set the LESSOPEN environment variable to lesspipe

First, make sure the following is set in the environment variable.

$ set | grep less
LESSOPEN='|/usr/bin/lesspipe.sh %s'

Please note that you can also do the following to setup the lesspipe.

$ eval "($lesspipe)"

$ cat ~/.bashrc
eval "($lesspipe)"

• lesspipe, lessfile are the input preprocessor for less, which lets it to open all types of files.
• lesspipe allows you to open while the process of conversion is going on using pipe.
• lessfile completes the conversion first, and then displays the content. This writes the converted thing to a temporary file then displays it.
• You can also write your own input preprocessor, and use it.

File Type 1: How to open a pdf file?

It shows all the text in the pdf file clearly, but ignores the images. The output may have some special characters here and there. But it is definitely readable.

File Type 1: How to open a pdf file?

It shows all the text in the pdf file clearly, but ignores the images. The output may have some special characters here and there. But it is definitely readable.

$ less Linux-101-Hacks.pdf
^LLinux 101 Hacks
www.thegeekstuff.com
o
o
o
Chapter 1: Powerful CD Command Hacks
cd is one of the most frequently used commands during a UNIX session.
The cd command hacks mentioned in this chapter will boost your productivity

File Type 2: How to open a word document file?

$ less pdb.doc
The Python Debugger Pdb
=======================

To use the debugger in its simplest form:

        >>> import pdb
        >>> pdb.run

The debugger's prompt is Pdb.  This will stop in the first
function call in

File Type 3: How to open a jpg, jpeg, png file?

While opening a image file (jpeg, jpg and png), less command shows the following information:

• Name of the file
• Type of file
• Number of pixels — width & height
• Size of the file

$ less testfile.jpeg
testfile.jpeg JPEG 2304x1728 2304x1728+0+0 DirectClass 8-bit 1.57222mb 0.550u 0:02

Note: Similar kind of information will be displayed for other image file types.

9. Less Command – Marked navigation

When you are viewing a large log file using less command, you can mark a particular position and return back to that place again by using that mark.

• ma – mark the current position with the letter ‘a’,
• ‘a – go to the marked position ‘a’.

10. Less Command – Multiple file paging

Method 1: You can open multiple files by passing the file names as arguments.

$ less file1 file2

Method 2: While you are viewing file1, use :e to open the file2 as shown below.

$ less file1
:e file2

Navigation across files: When you opened more than two files ( for e.g – less * ), use the following keys to navigate between files.

• :n – go to the next file.
• :p – go to the previous file.

October 15, 2019 in Learning, Tips and Tricks

How to convert MBps to IOPS or calculate IOPS from MB/s

Most SSDs have two speed ratings for reading as well as for writing.  The first rating is the sustained MB/s performance, which is the main marketing most manufacturers use.  The second rating is the 4K Random IOPS performance, which gives a much better idea of how the drive will perform in the real world.  The sustained MB/s rating is the sequential transfer rate the SSD will maintain continuously, such as over a period of 30 seconds.  The 4K Random IOPS on the other hand is how many 4K (4096 byte) operations the drive will handle per second with each block being read or written to a random position.

Usually when a Random 4K IOPS figure is given, it may state that this is at a certain queue depth, such as 4, 16, 32 or 64.  With a queue depth of 4, this means that there are 4 separate threads taking place with the drive, each thread independently running its own transfers.  With the use of Native Command Queuing (NCQ), the SSD can handle these threads simultaneously to improve the overall throughput compared to running a single thread.  While many hard disks use native command queuing to line up read/write operations to minimise seek times between each read/write operation, SSDs can read from and write to multiple NAND cells simultaneously, where as the read/write head in a hard disk can only be in one physical place at any time.
While it is nice to see how many IOPS a drive is capable of, it is also useful to see how this translates into actual throughput or even vice versa.  For example, most benchmark tools such as CrystalDiskMark and AS SSD report the random 4K performance in throughput, i.e. MB/s, while the SSD’s specifications usually rates the 4K performance in IOPS.To see how to translate MBps into IOPS and vice versa, we need to do a little math:

IOPS = (MBps Throughput / KB per IO) * 1024
Or
MBps = (IOPS * KB per IO) / 1024

So let’s say we have an SSD claiming a Random 4K write speed of 20,000 IOPS and it achieves 76.2MB/s in the CrystalDiskMark with the QD32 write test.

To convert the 76.2MB/s to IOPS, we perform the following calculation:

IOPS = (76.2 / 4) * 1024
IOPS = 19.1 * 1024
IOPS = 19,558.4

To see what throughput we need to achieve to match the actual 20,000 IOPS claim, we can perform this calculation in reverse:

MBps = (20,000 * 4) / 1024
MBps = 80,000 / 1024
MBps = 78.125MB/s

Note that each manufacturer uses its own method of coming up with their SSD IOPS ratings.  Besides separate IOPS ratings for read and write speeds, a given SSD can behave quite different depending on the type of data being read or written, as well as the duration this transfer takes place.  For example, an SSD that achieves 5,000 Random 4K IOPS sustained write over a period of 30 seconds may only achieve 1,000 IOPS sustained write over a period of 5 minutes.  For SSDs using the SandForce processor, the compressibility of the data also has an impact, so two benchmark tools may show completely different IOPS readings if one tool sends uncompressible data and the other tool sends highly compressible data and also if one runs the benchmark for longer duration than the other.

Happy calculating.