Change name of Variable while in a loop

Question

I have this idea in mind:

I have this number: CN=20

and a list=( "xa1-" "xa2-" "xb1-" "xb2-")

and this is my script:

for a in "${list[@]}"; do

        let "CN=$(($CN+1))"
        echo $CN

Output:
21
22
23
24

I am trying to create a loop where it creates the following variables, which will be referenced later in my script:

fxp0_$CN="fxp-$a$CN"

fxp0_21="fxp-xa1-21"
fxp0_22="fxp-xa2-22"
fxp0_23="fxp-xb1-23"
fxp0_24="fxp-xb2-24"

However, I have not been able to find a way to change the variable name within my loop. Instead, I was trying myself and I got this error when trying to change the variable name:

scripts/srx_file_check.sh: line 317: fxp0_21=fxp0-xa2-21: command not found

nickcrv06 · Accepted Answer · 2022-04-30 12:59:28Z

2

After playing around I found the solution!

for a in "${list[@]}"; do

        let "CN=$(($CN+1))"
        fxp_int="fxp0-$a$CN"
        eval "fxp0_$CN=${fxp_int}"
    done

    echo $fxp0_21
    echo $fxp0_22
    echo $fxp0_23
    echo $fxp0_24
    echo $fxp0_25
    echo $fxp0_26
    echo $fxp0_27
    echo $fxp0_28

Output:

fxp0-xa1-21
fxp0-xa2-22
fxp0-xb1-23
fxp0-xb2-24
fxp0-xc1-25
fxp0-xc2-26
fxp0-xd1-27
fxp0-xd2-28

answered Apr 30, 2022 at 12:59

nickcrv06

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Comments

markp-fuso · Accepted Answer · 2022-04-30 14:50:23Z

1

One common method for maintaining a dynamically generated set of variables is via arrays.

When the variable names vary in spelling an associative array comes in handy whereby the variable 'name' acts as the array index.

In this case since the only thing changing in the variable names is a number we can use a normal (numerically indexed) array, eg:

CN=20
list=("xa1-" "xa2-" "xb1-" "xb2-")

declare -a fxp0=()

for a in "${list[@]}"
do
    (( CN++ ))
    fxp0[${CN}]="fxp-${a}${CN}"
done

This generates:

$ declare -p fxp0
declare -a fxp0=([21]="fxp-xa1-21" [22]="fxp-xa2-22" [23]="fxp-xb1-23" [24]="fxp-xb2-24")

$ for i in "${!fxp0[@]}"; do echo "fxp0[$i] = ${fxp0[$i]}"; done
fxp0[21] = fxp-xa1-21
fxp0[22] = fxp-xa2-22
fxp0[23] = fxp-xb1-23
fxp0[24] = fxp-xb2-24

edited Apr 30, 2022 at 14:50

answered Apr 30, 2022 at 13:50

markp-fuso

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Comments

Dominique · Accepted Answer · 2022-04-30 12:00:18Z

0

As a general rule can I tell you that it's not a good idea to modify names of variables within loops.

There is, however, a way to do something like that, using the source command, as explained in this URL with some examples. It comes down to the fact that you treat a file as a piece of source code.

Good luck

answered Apr 30, 2022 at 12:00

Dominique

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