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
Env: GNU bash, version 4.3.11

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
Env: GNU bash, version 4.3.11

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