Add value to end of array

Shell Programming and Scripting
1

I'm trying to expand my array by adding another value onto the end of it, thus adding a new index and upping the length of the array by one. I am iterating through two arrays, and trying to get one array into the index of the other. I'm use 4.1.5 release of bash and most of the methods I have tried are outdated.

This is my code...

for ((i=1; i<=${COUNT1}; i++))
do
	for ((j=1; j<=${COUNT2}; j++))
	do
		if [[ ${MAIN_ARRAY} != ${SECOND_ARRAY[${j}]} ]]
		then
                      #Put the value of SECOND_ARRAY in MAIN_ARRAY
		fi
	done
done

I originally tried the += method and it did not work.

${ARRAY}+=${NEW_VALUE[${i}]}

Then I tried adding one to the length of the array.

q=`echo ${#ARRAY[@]}`
let q++ 
ARRAY[${q}]=${SECOND_ARRAY[${j}]}

Again, I am trying to iterate through two arrays, and if the the value of the second array is not in the first, put it in there at the end.

2

That arrays make loops such a pain is one reason I think they're overused.

A1="a b c d e f g"
A2=" q i u d e f g"

for X in $A1
do
        FOUND=0

        for Y in $A2
        do
                [ "$X" = "$Y" ] && FOUND=1
                [ "$FOUND" -gt 0 ] && break
        done

        [ "$FOUND" -eq 0 ] && A1="$A1 $X"
done

But if you must use arrays, that kind of loop works with them too:

for X in "${A1[@]}"
do
        FOUND=0

        for Y in "${A2[@]}"
        do
                [ "$X" = "$Y" ] && FOUND=1
                [ "$FOUND" -gt 0 ] && break
        done

        [ "$FOUND" -eq 0 ] && A1=( "${A1[@]}" $X )
done
3

One way with recent bash versions:

$ a1=( a b c d ) a2=( c d e f )
$ declare -p a1 a2
declare -a a1='([0]="a" [1]="b" [2]="c" [3]="d")'
declare -a a2='([0]="c" [1]="d" [2]="e" [3]="f")'
$ a1+=($( printf '%s\n' "${a2[@]}" | grep -Fxvf <( printf '%s\n' "${a1[@]}" )))
$ declare -p a1
declare -a a1='([0]="a" [1]="b" [2]="c" [3]="d" [4]="e" [5]="f")'

Values with special characters may need special attention.

P.S. declare -p is used only to display the content of the arrays.

1 Like
4

I'm new at bash, and do not understand some of your code.

What is the

[..]
[..]

in the for loop?

I'm assuming its like an if? Saying if X=Y then make found=1?

5

You already know what [ ] do if you've used if-statements before. It's actually an independent thing, if just makes use of it. It returns success when the statement within is true, or error when false.

&& is a short-form if-then. If the thing on the left returns success, run the thing on the right. || is the opposite -- if the thing on the left returns error, run the thing on the right.

true && echo "This will print"
false && echo "But this won't"

true || echo "This will not print"
false || echo "But this will"
1 Like