Bash – add a number to a variable

To add a number to a variable in bash, there are many approaches. Some of these are:

Declare variable as integer

Once a variable is is declared as integer (declare -i), the addition treats it as integer instead of string.

v=1
v+=1
echo "$v"
declare -i v
v=1
v+=1
echo "$v"

11
2

Use bash arithmetic expansion

Use $(()) for bash arithmetic expansion.

v=1
#both $v and v are ok in arithmetic expansion
a=$(($v+1))
b=$((v+1))
echo "$a"
echo "$b"

2
2