calculations in bash

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Arithmetic Operators Order of Precedence

Operators are evaluated in order of precedence. The levels are listed in order of decreasing precedence (quoting form the bash man page).

       id++ id--

              variable post-increment and post-decrement

       ++id --id

              variable pre-increment and pre-decrement

       - +    unary minus and plus

       ! ~    logical and bitwise negation

       **     exponentiation

       * / %  multiplication, division, remainder

       + -    addition, subtraction

       << >>  left and right bitwise shifts

       <= >= < >

              comparison

       == !=  equality and inequality

       &      bitwise AND

       ^      bitwise exclusive OR

       |      bitwise OR

       &&     logical AND

       ||     logical OR

       expr?expr:expr

              conditional operator

       = *= /= %= += -= <<= >>= &= ^= |=

              assignment

       expr1 , expr2

              comma

Arithmetic calculations using Inbuilt bash options

value1=5;value2=7

addition=$(( value1 + value2 ))

echo "$value1 + $value2 = $addition "

value1=5;value2=7

subtraction=$(( value1 - value2 ))

echo "$value1 - $value2 = $subtraction "

subtraction=$(( value2 - value1 ))

echo "$value2 - $value1 = $subtraction "

value1=5;value2=7

division=$(( value1 / value2 ))

echo "$value1 / $value2 = $division "

division=$(( value2 / value1 ))

echo "$value2 / $value1 = $division "

value1=5;value2=7

multiplication=$(( value1 * value2 ))

echo "$value1 * $value2 = $multiplication "

value1=5;value2=7

modulus=$(( value1 % value2 ))

echo "$value1 % $value2 = $modulus "

modulus=$(( value2 % value1 ))

echo "$value2 % $value1 = $modulus "

value1=5;value2=7

post_increment=$(( value1++ ))

echo "$value1 after post increment = $post_increment "

post_decrement=$(( value2-- ))

echo "$value2 after post decrement = $post_decrement "

value1=5;value2=7

pre_increment=$(( ++value1 ))

echo "$value1 after pre increment = $pre_increment "

pre_decrement=$(( --value2 ))

echo "$value2 after pre decrement = $pre_decrement "

value1=5;value2=7

exponentiation=$(( value1 ** value2 ))

echo "$value1 ** $value2 = $exponentiation "

exponentiation=$(( value2 ** value1 ))

echo "$value2 ** $value1 = $exponentiation "



Arithmetic calculations using let command

value1=5;value2=7

let addition=value1+value2

echo "$value1 + $value2 = $addition "

value1=5;value2=7

let subtraction=value1-value2

echo "$value1 - $value2 = $subtraction "

let subtraction=value2-value1

echo "$value2 - $value1 = $subtraction "

value1=5;value2=7

let division=value1/value2

echo "$value1 / $value2 = $division "

let division=value2/value1

echo "$value2 / $value1 = $division "

value1=5;value2=7

let multiplication=value1*value2

echo "$value1 * $value2 = $multiplication "

value1=5;value2=7

let modulus=value1%value2

echo "$value1 % $value2 = $modulus "

let modulus=value2%value1

echo "$value2 % $value1 = $modulus "

value1=5;value2=7

let post_increment=value1++

echo "$value1 after post increment = $post_increment "

let post_decrement=value2--

echo "$value2 after post decrement = $post_decrement "

value1=5;value2=7

let pre_increment=++value1

echo "$value1 after pre increment = $pre_increment "

let pre_decrement=--value2

echo "$value2 after pre decrement = $pre_decrement "

value1=5;value2=7

let exponentiation=value1**value2

echo "$value1 ** $value2 = $exponentiation "

let exponentiation=value2**value1

echo "$value2 ** $value1 = $exponentiation "

Arithmetic calculations using expr command

value1=5;value2=7

addition=$( expr $value1 + $value2 )

echo "$value1 + $value2 = $addition "

value1=5;value2=7

subtraction=$( expr $value1 - $value2 )

echo "$value1 - $value2 = $subtraction "

subtraction=$( expr $value2 - $value1 )

echo "$value2 - $value1 = $subtraction "

value1=5;value2=7

division=$( expr $value1 / $value2 )

echo "$value1 / $value2 = $division "

division=$( expr $value2 / $value1 )

echo "$value2 / $value1 = $division "

value1=5;value2=7

multiplication=$( expr $value1 \* $value2 )

echo "$value1 * $value2 = $multiplication "

value1=5;value2=7

modulus=$( expr $value1 % $value2 )

echo "$value1 % $value2 = $modulus "

modulus=$( expr $value2 % $value1 )

echo "$value2 % $value1 = $modulus "

Arithmetic calculations using bc command

value1=5;value2=7

addition=$( echo $value1+$value2 |bc )

echo "$value1 + $value2 = $addition "

value1=5;value2=7

subtraction=$( echo $value1-$value2 |bc )

echo "$value1 - $value2 = $subtraction "

subtraction=$( echo $value2-$value1 |bc )

echo "$value2 - $value1 = $subtraction "

value1=5;value2=7

division=$( echo $value1/$value2 |bc )

echo "$value1 / $value2 = $division "

division=$( echo $value2/$value1 |bc )

echo "$value2 / $value1 = $division "

value1=5;value2=7

multiplication=$( echo $value1*$value2 |bc )

echo "$value1 * $value2 = $multiplication "

value1=5;value2=7

modulus=$( echo $value1%$value2 |bc )

echo "$value1 % $value2 = $modulus "

modulus=$( echo $value2%$value1 |bc )

echo "$value2 % $value1 = $modulus "

References :- http://www.softpanorama.org/Scripting/Shellorama/arithmetic_expressions.shtml

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du command one liners

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To display disk usage for a folder in human readable format

# du -h /home

To display disk usage for a folder in human readable format (including all subdirectories along with hidden files)

# du -ah /home

To display disk usage for a folder in KB

# du -k /home

To display disk usage for a folder in MB

# du –m /home

To display disk usage in human readable format and total at end line

# du –ch /home

To display disk usage by excluding some files or folders

# du -ah --exclude="*.txt" /home/

To display the disk usage based on modification of time, use the flag “–time”

# du -ha --time /home/

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free command one liners

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Default free shows memory statistics in KB

# free

To see memory statistics in Bytes

# free -b

To see memory statistics in KB

# free -k

To see memory statistics in MB

# free -m

To see memory statistics in GB

# free -g

To see memory statistics with total line

# free -t

To see memory statistics by disabling buffer adjusted line

# free -o

To repeat free command n seconds infinitly

# free -g -s 5

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sort command one liners

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sort in default mode sorts the file in alphabetical order

# sort file_name

sort removes the duplicates using the -u option

# sort -u file_name

The default sort 'might' give incorrect result on a file containing only numbers, so to work bet on such file -n option can be used

# sort -n file_name

sort file numerically in reverse order using option -r

# sort -nr file_name

sort can sort multiple files as well.

# sort -n file_name1 file_name2

Sort can merge two files and remove duplicates

# sort -nu file_name 1 file_name 2

Sorting a file containing multiple fields, default sort will sort by first column

# sort file_name

sort file on the basis of 1st field delimited by “,”

# sort -t"," -k1,1 file_name

Where,

'-t' option is used to provide the delimiter in case of files with delimiter.

'-k' is used to specify the keys on the basis of which the sorting has to be done.

The format of '-k' is : '-km,n' where m is the starting key and n is the ending key.

Sorting file on the basis of the 2nd field delimited by “:”

# sort -t":" -k2,2 file_name

Sorting file on the basis of 2nd field , numerically:

# sort -t"," -k2n,2 file_name

Remove duplicates from the file based on 1st field delimited by “|”

# sort -t"|" -k1,1 -u file_name

Sort the file numerically on the 2nd field in reverse order delimited by “;”

# sort -t";" -k2nr,2 file_name

Sort the file alphabetically on the 1st field, numerically on the 2nd field delimited by “,”

# sort -t"," -k1,1 -k2n,2 file_name

sort a file based on the 1st and 2nd field, and numerically on 3rd field on  a file containing 5 columns:

# sort -t"," -k1,2 -k3n,3 file_name

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