Multiplying array element

Shell Programming and Scripting
1

I am trying to take all the elements of an array and multiply them by 2, and then copy them to a new array. Here is what I have

i=0
for true in DMGLIST[@]
	do
	let DMGSIZES2="${DMGSIZES}"*2
	let i++
done
unset i

echo ${DMGSIZES2[@]}

It does the calculation correctly for the first element, but after that it doesn't return anything at all. DMGSIZES2 seems to have only one element.

I have also tried it without quotes, but I get the same problem.

Any insight is appreciated. Also, any suggestions for better ways to do this are welcome. Thanks!

2

What contains DMGLIST ?
true as a variable name is odd.

3

I don't think I understand how thr variable fits in here. I have read a bunch of tutorials, but I just don't understand. For me it seems to get in the way, although obviously I did it wrong here. Can someone explain?

4

Please post a complete script. Without knowing what is in your arrays, it's difficult to figure out the issue.

5

Are you just trying to double number in an array and copying it to another array?

DMGLIST=(1 2 3 4)
for (( i = 0 ; i < "${#DMGLIST[@]}"; i++ )) 
do
    DMGLIST2[$i]=$((${DMGLIST[$i]}*2))
    echo "${DMGLIST2[$i]}";
done
6 
[root@~]# bash array.sh 
2 4 6
[root@~]# cat array.sh 
#!/bin/bash
b=(1 2 3)
a=0
for i in ${b[@]}
do
    narray[${a}]=$((${b[$a]}*2))
    ((a++))
done
echo ${narray[@]}
 
Test environment : centos 5.5 64bit
GNU bash, version 3.2.25
7

Or

#!/bin/bash
b=(2 4 6)
a=0
for i in ${b[@]}
do
    narray[a++]=$((i*2))
done
echo ${narray[@]}
2 Likes
8

Perfect. I'm sure the other scripts accomplished the same thing, but this works and I understand it, and it demonstrates how to use the variable properly. Thanks so much!