eval array value bash

Question

I am trying to substitute both the array name and value using eval and losing my mind with combinations that are not working

 $ eval echo \$${port[$index]}${item[0]}${item[8]}
   some_value

declare -a port=('Ex' 'backup' 'DRAC' 'Service');
declare -a item=('net' 'switch' 'port' 'speed' 'cvsswitch' 'vlan' 'link' 'count' 'list')

       for x in $(eval echo \$${port[$index]}${item[0]}${item[8]}) ; do
           eval ${port[$index]}${item[7]}=$[${port[$index]}${item[7]} +1]                                      # incriment count
           eval echo \$${port[$index]}${item[7]}                                                               # set count
           eval \$"${port[$index]}${item[1]}"[\$${port[$index]}${item[7]}]   <---- not working
       done
fi

I am getting the following output when trying to eval this statement to assign the array[index_value] a value.

$ eval \$${port[$index]}${item[1]}[\$${port[$index]}${item[7]}]=abc123
-bash: [1]: command not found
or
$ eval \$${port[$index]}${item[1]}[\$${port[$index]}${item[7]}]=abc123
-bash: [1]=abc123: command not found

Does anyone have advice on how to get this working?

Thanks!

What if we stop talking about eval, and ask clearly about the thing you're trying to accomplish, rather than the tool you want to do it with? — Charles Duffy
– Charles Duffy, Commented Feb 25, 2014 at 23:49
For instance, when you say eval \$${port[$index]}${item[1]}[\$${port[$index]}${item[7]}]=abc123 -- what, exactly, do you expect that to actually do? — Charles Duffy
– Charles Duffy, Commented Feb 25, 2014 at 23:51

Charles Duffy · Accepted Answer · 2014-02-25 23:58:35Z

1

You don't need eval, and shouldn't use eval, for assignments of this type.

declare -a port=('Ex' 'backup' 'DRAC' 'Service')
declare -a item=('net' 'switch' 'port' 'speed' 'cvsswitch' 'vlan' 'link' 'count' 'list')

index=3 # for example
array_name=${port[$index]}${item[1]}
array_idx=${port[$index]}${item[7]}

declare -A "$array_name" # since your index is non-numeric
printf -v "${array_name}[${array_idx}]" '%s' abc123

This will set Serviceswitch[Servicecount] to abc123.

Assigning your variable names ahead-of-time is better practice anyhow -- makes it easier to diagnose why something failed when you can look at the pieces that built up to it.

See BashFAQ #6 for an exhaustive treatment of the subject, including portability discussion.

edited Feb 25, 2014 at 23:58

answered Feb 25, 2014 at 23:53

Charles Duffy

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eval array value bash

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