Loop through array, assign new value to variable in array

Question

In my script I ask the user for some input and save it into some variables. Before using the strings in the variables I want to cut them if they are too long and add an ellipsis at the end. So I put all of the variables in an array and send them through a loop and an if statement and reasign the new value to the variable in the array. I have tried many ways and none have worked. The following being an example:

preset1="Short string"
preset2="Not long very string"
preset3="A very long string here which we will then cut"

presets=("${preset1}" "${preset2}" "${preset3}")

for x in "${presets[@]}"; do
    if [[ "${#x}" -gt 20 ]]; then
        y="${x:0:20}..."
        presets[$x]="$y"
    fi
done

Please help!

PesaThe · Accepted Answer · 2017-12-28 23:48:31Z

2

You have to loop over indexes of your array in order to change the values:

for x in "${!presets[@]}"; do
    str=${presets[$x]}
    (( ${#str} > 20 )) && presets[$x]="${str:0:20}..."
done

Works for associative and sparse arrays as well.

For variety, you can also use only parameter expansion like this:

for x in "${!presets[@]}"; do
    str=${presets[$x]}
    suffix=${str:20}
    presets[$x]=${str:0:20}${suffix:+...}
done

edited Dec 28, 2017 at 23:48

answered Dec 28, 2017 at 2:28

PesaThe

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5 Comments

vato Over a year ago

This and the next solution work, but the variables e.g.: ${preset3} do not change. Using bash -x you can see that the string gets cut and the ellipsis added, but you can see that the value of the variable does not get updated if you do: echo ${preset3}.

PesaThe Over a year ago

@vato And why exactly would you like to do that? Isn't changing the array items enough?

PesaThe Over a year ago

@vato note that you can also use arrays directly with read: IFS= read -r 'array[0]'. You don't need variables at all. Just keep the array if it's more convenient for you.

vato Over a year ago

I will try and explain what it is that I'm trying to achieve. In one part of the script I ask the user for the names of the presets. These presets cannot be too long because I use them in a little menu I print out for the user in a later step of the script. I could of course use an if statement for every preset and cut the strings there. I just thought, naively, that it might be easier putting everything in an array an use a for loop.

PesaThe Over a year ago

@vato I understand. But why not use just the array for everything? Why do you want to change even the variables. Creating menus will also be much easier using a list of options in an array.

vato · Accepted Answer · 2017-12-28 07:36:13Z

1

You need to use the array[i] syntax to assign to array elements:

for ((i = 0; i < ${#presets[@]}; ++i)); do
    x=${presets[i]}
    if [[ "${#x}" -gt 20 ]]; then
        y="${x:0:20}..."
        presets[i]="$y"
    fi
done

edited Dec 28, 2017 at 7:36

vato

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answered Dec 28, 2017 at 2:29

user8680478

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