Array intersection in Bash [duplicate]

Solution 1:

The elements of list 1 are used as regular expression looked up in list2 (expressed as string: ${list2[*]} ):

list1=( 1 2 3 4   6 7 8 9 10 11 12)
list2=( 1 2 3   5 6   8 9    11 )

l2=" ${list2[*]} "                    # add framing blanks
for item in ${list1[@]}; do
  if [[ $l2 =~ " $item " ]] ; then    # use $item as regexp
    result+=($item)
  fi
done
echo  ${result[@]}

The result is

1 2 3 6 8 9 11

Solution 2:

Taking @Raihan's answer and making it work with non-files (though FDs are created) I know it's a bit of a cheat but seemed like good alternative

Side effect is that the output array will be lexicographically sorted, hope thats okay (also don't kno what type of data you have, so I just tested with numbers, there may be additional work needed if you have strings with special chars etc)

result=($(comm -12 <(for X in "${array1[@]}"; do echo "${X}"; done|sort)  <(for X in "${array2[@]}"; do echo "${X}"; done|sort)))

Testing:

$ array1=(1 17 33 99 109)
$ array2=(1 2 17 31 98 109)

result=($(comm -12 <(for X in "${array1[@]}"; do echo "${X}"; done|sort)  <(for X in "${array2[@]}"; do echo "${X}"; done|sort)))

$ echo ${result[@]}
1 109 17

p.s. I'm sure there was a way to get the array to out one value per line w/o the for loop, I just forget it (IFS?)

Solution 3:

Your answer won't work, for two reasons:

• $array1 just expands to the first element of array1. (At least, in my installed version of Bash that's how it works. That doesn't seem to be a documented behavior, so it may be a version-dependent quirk.)
• After the first element gets added to result, result will then contain a space, so the next run of result=$result" "$item1 will misbehave horribly. (Instead of appending to result, it will run the command consisting of the first two items, with the environment variable result being set to the empty string.) Correction: Turns out, I was wrong about this one: word-splitting doesn't take place inside assignments. (See comments below.)

What you want is this:

result=()
for item1 in "${array1[@]}"; do
    for item2 in "${array2[@]}"; do
        if [[ $item1 = $item2 ]]; then
            result+=("$item1")
        fi
    done
done