Bash find unique values in array1 not in array2 (and vice-versa)

user_4542117 0
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In bash, I know to be able to find the unique values between two arrays can be found by:

echo "${array1[@]} ${array2[@]}" | tr ' ' '\n' | sort | uniq -u

However, this gives the unique values between BOTH arrays. What if I wanted something about the elements that are unique only to array1 and elements that are unique only to array2? For example:

array1=(1 2 3 4 5)
array2=(2 3 4 5 6)

original_command_output = 1 6
new_command_output1 = 1
new_command_output2 = 6
unique arrays bash
3 Answers

comm is probably the way to go but if you're running bash >= 4 then you can do it with associative arrays:

#!/bin/bash

declare -a array1=(1 2 3 4 5) array2=(2 3 4 5 6)
declare -A uniq1=() uniq2=()

for e in "${array1[@]}"; do uniq1[$e]=; done
for e in "${array2[@]}"; do
    if [[ ${uniq1[$e]-1} ]]
    then
        uniq2[$e]=
    else
        unset "uniq1[$e]"
    fi
done

echo "new_command_output1 = ${!uniq1[*]}"
echo "new_command_output2 = ${!uniq2[*]}"

new_command_output1 = 1
new_command_output2 = 6
user_33877160

You could use the comm command.

To get elements unique to the first array:

comm -23  \
    <(printf '%s\n' "${array1[@]}" | sort) \
    <(printf '%s\n' "${array2[@]}" | sort)

and elements unique to the second array:

comm -13  \
    <(printf '%s\n' "${array1[@]}" | sort) \
    <(printf '%s\n' "${array2[@]}" | sort)

Or, more robust, allowing for any character including newlines to be part of the elements, split on the null byte:

comm -z -23  \
    <(printf '%s\0' "${array1[@]}" | sort -z) \
    <(printf '%s\0' "${array2[@]}" | sort -z)
user_32668470

BASH builtins can handle this cleaner and quicker. This will read both arrays for each element, comparing if they exist in either. If no match is found, output unique elements

arr1=(1 2 3 4 5) arr2=(1 3 2 4)

for i in "${arr1[@]}" "${arr2[@]}" ; do
        [[ ${arr2[@]} =~ $i ]] || echo $i
        [[ ${arr1[@]} =~ $i ]] || echo $i
done

output: 5

If one of yours arrays have multiple character elements, e.g. 152, then you must convert the arrays, adding a literal character before and after. This way regex can identify an exact match

arr1=(1 2 3 4 5) arr2=(1 3 2 4 152)

for i in "${arr1[@]}" ; do
     var1+="^$i$"
done

for i in "${arr2[@]}" ; do
     var2+="^$i$"
done

for i in "${arr1[@]}" "${arr2[@]}" ; do
        [[ $var1 =~ "^$i$" ]] || echo $i
        [[ $var2 =~ "^$i$" ]] || echo $i
done

output: 5 152

user_155421360
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