How to parse $QUERY_STRING from a bash CGI script?

Try this:

saveIFS=$IFS
IFS='=&'
parm=($QUERY_STRING)
IFS=$saveIFS

Now you have this:

parm[0]=a
parm[1]=123
parm[2]=b
parm[3]=456
parm[4]=c
parm[5]=ok

In Bash 4, which has associative arrays, you can do this (using the array created above):

declare -A array
for ((i=0; i<${#parm[@]}; i+=2))
do
    array[${parm[i]}]=${parm[i+1]}
done

which will give you this:

array[a]=123
array[b]=456
array[c]=ok

Edit:

To use indirection in Bash 2 and later (using the parm array created above):

for ((i=0; i<${#parm[@]}; i+=2))
do
    declare var_${parm[i]}=${parm[i+1]}
done

Then you will have:

var_a=123
var_b=456
var_c=ok

You can access these directly:

echo $var_a

or indirectly:

for p in a b c
do
    name="var$p"
    echo ${!name}
done

If possible, it’s better to avoid indirection since it can make code messy and be a source of bugs.