Arithmetic Expansion

Remarks#

Numbers in arithmetic expansions must match the following ERE:

[-+]?(0[0-7]+|[1-9][0-9]*|0[Xx][0-9A-Fa-f]+)

Arithmetic expressions support signed integer operators, comparisons, Boolean expressions, assignments, and ternary expressions from C.

Resources

Line Count

i=0
while read -r line; do
        i=$((i+1))
done < file
echo $i

With a file containing:

Alpha
Beta
Gamma
Delta
Epsilon

The above script prints: 5

Parameter Expansion

Loop n times:

while [ $((i=${i:=0}+1)) -le "$n" ]; do
    echo line $i
done

Output for n=5:

line 1
line 2
line 3
line 4
line 5

Manipulating decimals:

$ i=3.14159; echo $((${i%.*}*2))
6
$ i=3.14159; echo $((${i#*.}*2))
28318

Ternery Expressions

Absolute value:

$ for n in -8 -2 0 3 4; do
>     echo $((n<0?-n:n))
> done
8
2
0
3
4

Fix variable range:

$ min=2
$ max=4
$ for n in 1 2 3 4 5; do
>     echo $((n<min?min:n>max?max:n))
> done
2
2
3
4
4

Is a Power of 2

$ ispow2() { return $((!($1!=0&&($1&$1-1)==0))); }
$ i=0
$ while [ $i -lt 100 ]; do
>     if ispow2 $((i=i+1)); then
>         echo $i
>     fi
> done
1
2
4
8
16
32
64

$1!=0 0 is not a power of 2.

($1&$1-1)==0 Unset the lowest bit. If it was the only bit then the number was a power of 2.

The additional ! was for correcting the value to what the shell expects, which is the opposite of the conventional true/false values (zero for true and non-zero for false, vs zero for false and non-zero for true).