How to change the value of value in BASH ??

Question

Hello All,

Let's say i have the Following,

Vegetable=Potato ( Kind of vegetable that i have )

Potato=3 ( quantity available )

If i wanna know how many vegetables i have (from a script where i have access only to variable Vegetable), i do the following:

Quantity=${!Vegetable}

But let's say i take one Potato then i want to update the quantity, i should be able to do the following:

${Vegetable}=$(expr ${!Vegetable} - 1)

It does not work !!

Any clues to realize this

Thanks

Answer 1

eval ${Vegetable}=$(expr ${!Vegetable} - 1) 

Answer 2

with bash 4.0 you can make use of associative arrays

declare -A VEGETABLE
VEGETABLE["Potato"]=3
VEGETABLE["Potato"]=$((VEGETABLE["Potato"]-1))
echo ${VEGETABLE["Potato"]}

Answer 3

Try:

declare $Vegetable=$((${!Vegetable} - 1))

You don't need to use expr, by the way. As you can see, Bash can handle integer arithmetic.

See this page for more information on indirection in Bash.