Re: create variables in a loop?

On 29.05.2024 12:57, Dr Eberhard W Lisse wrote:

Hi,
 
I would like to do something like
 
for i in USD GBP
do
$i=somevalue
done
 
does not work, of course.
 
Any idea on how to create (and fill variables through a loop)?

You've already got the technical answer to your (literal) question.
Basically something like

    for currency in USD GBP EUR
    do
        eval "${currency}='some value $((++n))'"
    done
    printf "%s\n" "$USD" "$GBP" "$EUR"

But I suggest to reconsider your software design approach!

Mind that variables are for programmers, and that if you create
variable names dynamically you either have to hard code the names
in several places, or use 'eval' in several places; where ever you
want to access them. (Which requires additional tests, to be sure.)

Other approaches are (for example) defining data structures for
the allowed variable name values (and attributes)

    currencies=( USD GBP EUR )
    factor=( 1.2 1.5 1.0 )

    value=4.3
    for (( i = 0; i < ${#currencies[@]} ; i++ ))
    do
        printf "%s: %g\n" "${currencies[i]}" $(( ${value} * ${factor[i]} ))
    done

or use control constructs (to differentiate interrogated dynamic
name values) like

    for f in data_file_*
    do
        curr=${f##data_file_}
        case ${curr} in
        (USD)   val=1.2 ;;
        (GBP)   val=1.5 ;;
        (EUR)   val=1.0 ;;
        (*)     exit 1 ;;
        esac
    done

to be able to tell apart allowed values from undefined and errors.

The question is; do I really want an *individual* _variable name_
created? (Or is the technical [variable] name actually just data?)

Janis

 
greetings, el