TECHPULP | Arithmetic operation using double parentheses construct in Bash

October 18, 2008

By: Neo

In Category Bash

The following script illustrates how double parentheses can be used to do arithmetic operations.

#!/bin/sh

(( a = 23 ))
echo "a (assign value) = $a"

(( ++a ))
echo "a (after ++a) = $a"

(( --a ))
echo "a (after --a) = $a"

(( a++ ))
echo "a (after a++) = $a"

(( a-- ))
echo "a (after a--) = $a"

echo

(( b = a>30?12:20 ))
echo "If a > 30, then b = 12, else b = 20."
echo "b = $b "

echo

The following is output of the above script.

[neo@techpulp ~]# sh dpara.sh
a (assign value) = 23
a (after ++a) = 24
a (after --a) = 23
a (after a++) = 24
a (after a--) = 23

If a > 30, then b = 12, else b = 20.
b = 20

[neo@techpulp ~]#

Here is an another example to use at shell prompt.

[neo@techpulp ~]# echo $((24/12))
2
[neo@techpulp ~]#

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