Compare/Difference of two arrays in Bash

Question

Is it possible to take the difference of two arrays in Bash. What is a good way to do it?

Code:

Array1=( "key1" "key2" "key3" "key4" "key5" "key6" "key7" "key8" "key9" "key10" ) Array2=( "key1" "key2" "key3" "key4" "key5" "key6" )   Array3 =diff(Array1, Array2)  Array3 ideally should be : Array3=( "key7" "key8" "key9" "key10" ) 

Answer 1

echo ${Array1[@]} ${Array2[@]} | tr ' ' '\n' | sort | uniq -u 

Output

key10 key7 key8 key9 

You can add sorting if you need

Answer 2

If you strictly want Array1 - Array2, then

Array1=( "key1" "key2" "key3" "key4" "key5" "key6" "key7" "key8" "key9" "key10" ) Array2=( "key1" "key2" "key3" "key4" "key5" "key6" )  Array3=() for i in "${Array1[@]}"; do     skip=     for j in "${Array2[@]}"; do         [[ $i == $j ]] && { skip=1; break; }     done     [[ -n $skip ]] || Array3+=("$i") done declare -p Array3 

Runtime might be improved with associative arrays, but I personally wouldn't bother. If you're manipulating enough data for that to matter, shell is the wrong tool.

---

For a symmetric difference like Dennis's answer, existing tools like comm work, as long as we massage the input and output a bit (since they work on line-based files, not shell variables).

Here, we tell the shell to use newlines to join the array into a single string, and discard tabs when reading lines from comm back into an array.

 $ oldIFS=$IFS IFS=$'\n\t' $ Array3=($(comm -3 <(echo "${Array1[*]}") <(echo "${Array2[*]}"))) comm: file 1 is not in sorted order $ IFS=$oldIFS $ declare -p Array3 declare -a Array3='([0]="key7" [1]="key8" [2]="key9" [3]="key10")' 

It complains because, by lexographical sorting, key1 < … < key9 > key10. But since both input arrays are sorted similarly, it's fine to ignore that warning. You can use --nocheck-order to get rid of the warning, or add a | sort -u inside the <(…) process substitution if you can't guarantee order&uniqueness of the input arrays.