Ubuntu – sort command : -g versus -n flag

command line

What's the difference between using the sort command with -g and -n?

I have tried both flags with ls -la and the output was identical.

The man-page says that -g "compares according to general numerical value" and -n "compares according to string numerical value" ?

I don't get what they mean there.

What does "general numerical value" mean? What does "string numerical value" mean?

Best Answer

From sort info page, sort -g is explained by these

‘-g’
‘--general-numeric-sort’
‘--sort=general-numeric’
     Sort numerically, converting a prefix of each line to a long
     double-precision floating point number.  *Note Floating point::.
     Do not report overflow, underflow, or conversion errors.  Use the
     following collating sequence:

        • Lines that do not start with numbers (all considered to be
          equal).
        • NaNs (“Not a Number” values, in IEEE floating point
          arithmetic) in a consistent but machine-dependent order.
        • Minus infinity.
        • Finite numbers in ascending numeric order (with -0 and +0
          equal).
        • Plus infinity.

     Use this option only if there is no alternative; it is much slower
     than ‘--numeric-sort’ (‘-n’) and it can lose information when
     converting to floating point.

sort -n is the natural sort we usually expect

‘-n’
‘--numeric-sort’
‘--sort=numeric’
     Sort numerically.  The number begins each line and consists of
     optional blanks, an optional ‘-’ sign, and zero or more digits
     possibly separated by thousands separators, optionally followed by
     a decimal-point character and zero or more digits.  An empty number
     is treated as ‘0’.  The ‘LC_NUMERIC’ locale specifies the
     decimal-point character and thousands separator.  By default a
     blank is a space or a tab, but the ‘LC_CTYPE’ locale can change
     this.

     Comparison is exact; there is no rounding error.

     Neither a leading ‘+’ nor exponential notation is recognized.  To
     compare such strings numerically, use the ‘--general-numeric-sort’
     (‘-g’) option.

Check Steeldriver's answer for a better explanation.

Related Solutions

Ubuntu – Difference between echo -e “” and echo $“”

echo -e and echo $'...' are both similar in that they support the following escape sequences:

  \a     alert (bell)
  \b     backspace
  \e
  \E     an escape character
  \f     form feed
  \n     new line
  \r     carriage return
  \t     horizontal tab
  \v     vertical tab
  \\     backslash
  \0nnn  the eight-bit character whose value is the octal value nnn (zero to three octal digits)
  \xHH   the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
  \uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)
  \UHHHHHHHH
         the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)

They do have differences. In addition to the above, echo -e supports:

  \c     suppress further output
  \0nnn  the eight-bit character whose value is the octal value nnn (zero to three octal digits)

By contrast, $'....' supports:

 \'     single quote
 \"     double quote
 \nnn   the eight-bit character whose value is the octal value nnn (one to three digits)
 \cx    a control-x character

Observe that, between the two, the \c extensions are incompatible:

$ echo -e  'start\n\cIstop'
start
$ echo  $'start\n\cIstop'
start
        stop

For echo -e above, \c suppresses further output, thereby ignoring the Istop. By contrast, for $'...', the \cI is interpreted as a tab.

The visually-similar form: `$"..."`

By contrast with $'...', the function of $"..." is quite different. It will cause the string it contains to be translated according to the current locale.

The `echo -e` controversy

echo -e is not universally supported by shells and many regard the -e option as a design mistake. Observe:

$ ls
-e  -n
$ echo *
$ printf "%s\n" *
-e
-n

As you can see, if what you are printing with echo starts with a dash, the results can be unexpected. Unless you are sure that the first string that you will print with echo does not start with a dash, you are likely better off using printf.

For these reasons, the POSIX standard concludes:

New applications are encouraged to use printf instead of echo.

Chet Ramey, who has maintained bash for the last 22 years, agrees:

[N]ew code should use printf.

Ubuntu – Difference between $ and # in Linux environment

In short, if the screen shows a dollar sign ($) or hash (#) on the left of the blinking cursor, you are in a command-line environment.

$, #, % symbols indicate the user account type you are logged in to.

Dollar sign ($) means you are a normal user.
hash (#) means you are the system administrator (root).
In the C shell, the prompt ends with a percentage sign (%).

There are differences on prompts in different Unix or GNU/Linux distributions because of their default settings. For example, the prompt of Debian/Ubuntu is guest@linux:~$, the one of Fedora/CentOS/RedHat is [guest@linux ~]$ and the one of SuSE Linux/OpenSUSE is guest@linux:~>. In general, the prompt usually show the login user name, machine hostname, and current working directory and ended with a dollar ($), percentage (%), or hash (#) sign.

guest@linux:~$

guest - username: the user account you are logged in to.
linux - machine hostname: the machine you are operating.
~ - current working directory: the directory you are in. Tilde (~) means home directory, i.e. the default directory when first logging in.

Reference: wiki.debian.org.hk/w/Basic_Command_Line

Best Answer

Related Solutions

Ubuntu – Difference between echo -e “” and echo $“”

The visually-similar form: $"..."

The echo -e controversy

Ubuntu – Difference between $ and # in Linux environment

Related Question

The visually-similar form: `$"..."`

The `echo -e` controversy