Bash += and -=

External

• https://linuxize.com/post/bash-increment-decrement-variable/

Internal

• bash Concepts
• ((...))

Overview

+= and -= are assignment operators that can be used to increment/decrement the value of the left operand with the value specified after the operator. The operators can be used on integral values as such:

i=0
((i+=1))
echo ${i}

displays:

1

Also:

i=0
((i-=1))
echo ${i}

displays:

-1

+= can be used on string values as such:

s="something"
s+=" else"
echo ${s}

displays:

something else

-= does not work with strings.