Bash-扩展变量嵌套在变量中

Question

Noble StackOverflow readers,

I have a comma seperated file, each line of which I am putting into an array. Data looks as so...

25455410,GROU,AJAXa,GROU1435804437
25455410,AING,EXS3d,AING4746464646
25455413,TRAD,DLGl,TRAD7176202067

There are 103 lines and I am able to generate the 103 arrays without issue.

n=1; while read -r OrdLine; do
    IFS=',' read -a OrdLineArr${n} <<< "$OrdLine"
    let n++
done < $WkOrdsFile

HOWEVER, I can only access the arrays as so...

echo "${OrdLineArr3[0]}  <---Gives 25455413

I cannot access it with the number 1-103 as a variable - for example the following doesn't work...

i=3
echo "${OrdLineArr${i}[0]}

That results in...

./script2.sh: line 24: ${OrdLineArr${i}[0]}: bad substitution

I think that the answer might involve 'eval' but I cannot seem to find a fitting example to borrow. If somebody can fix this then the above code makes for a very easy to handle 2d array replacement in bash!

Thanks so much for you help in advance!

Dan

Answer 1

You can use indirect expansion . For example, if $key is OrdLineArr4[7] , then ${!key} (with an exclamation point) means ${OrdLineArr4[7]} . (See §3.5.3 "Shell Parameter Expansion" in the Bash Reference Manual , though admittedly that passage doesn't really explain how indirect expansion interacts with arrays.)

I'd recommend wrapping this in a function:

function OrdLineArr () {
    local -i i="$1"          # line number (1-103)
    local -i j="$2"          # field number (0-3)
    local key="OrdLineArr$i[$j]"
    echo "${!key}"
}

Then you can write:

echo "$(OrdLineArr 3 0)"        # prints 25455413
i=3
echo "$(OrdLineArr $i 0)"       # prints 25455413

This obviously isn't a total replacement for two-dimensional arrays, but it will accomplish what you need. Without using eval .

Answer 2

eval通常不是一个好主意，但是您可以使用以下方法实现：

eval echo "\${OrdLineArr$i[0]}"

Answer 3

I would store each line in an array, but split it on demand:

readarray OrdLineArr < $WkOrdsFile
...
OrdLine=${OrdLineArr[i]}
IFS=, read -a Ord <<< "$OrdLine"

However, bash isn't really equipped for data processing; it's designed to facilitate process and file management. You should consider using a different language.