Compare bash arrays issue

UNIX for Beginners Q & A
1

Hello everyone,
I need help comparing 2 arrays. the first array is static; the second array is not ..

array1=( "macOS Mojave" "iTunes" )
cd /Volumes
array2=( * )

# output of array2

macOS Mojave
iTunes
Mac me

The problem occurs when I compare the arrays with the following code -

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

for x in "${DIFF[@]}"
        do
                echo -e "$x"
        done

# wrong result

Mac
me

# desired result

Mac me

I'm sending the output via email and it still splits up "Mac" "me" on separate lines. How could I keep the DIFF array intact? Not separating the words when I do the compare?

2

Indeed, the operation should be line based, rather than word based, since file names can have spaces in them.

Compare:

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

with:

printf "%s\n" "${array1[@]}" "${array2[@]}" | sort | uniq -u

--
Note: File names could even have newlines in them, but it is rare so let's leave that for now......

1 Like
4

$DIFF in not an array but a scalar variable.
Try also

IFS=$'\n'
echo "${array1
[*]}"$'\n'"${array2
[*]}" | sort | uniq -u
Mac me

Don't forget to reset IFS to your default value.

1 Like
5

Your suggestions work for outputting to standard output but as I was testing the email portion, if there are 2 entries as differences - it treated them as 1 element in the array as oppose to 2 elements. I was hoping to have both differences in the array as its own element.

length=${#DIFF[@]}
for (( i=0; i<${length}; i++ ));
do
echo ${DIFF}
done

# wrong result

DIFF[0] Mac me 
Windows
DIFF[0] Mac me Windows

# Desired result

DIFF[0] Mac me
DIFF[1] Windows
6

Again: DIFF is a scalar NOT an array the way you create / populate it. There is NO ${DIFF[1]} !

Wouldn't it be better to show the big picture of your problem, so a tailored solution can be found? What are you after, in the end?

7

Here is the code I'm working on. After comparing both arrays, if multiple differences are detected between arr1 and arr2. I should be able to send an email for each difference found. Below, looks like I'm still treating the scalar as an array? Is there a way to make the scalar into array after comparing so I can access the elements individually?

arr1=( "macOS Mojave" "iTunes" )
cd /Volumes
arr2=( * )

IFS=$'\n'
DIFF=`echo "${arr1[*]}"$'\n'"${arr2[*]}" | sort | uniq -u`
VOLCOUNT=`printf "%s\n" "${arr1[@]}" "${arr2[@]}" | sort | uniq -u | wc -l`
if [ "$VOLCOUNT" -gt "$COUNT" ]; then
        for x in "${DIFF[@]}"
        do
                echo -e "To: ${TO}\nSubject: Alert: ${SUBJECT}$x \n\n$SIGN" | $MAIL -a gmail ${TO}
        done
else
        >/dev/null 2>&1
fi
unset $IFS
exit 0
8

Yes. You did it twice with arr1 and arr2 . It can vary from shell to shell, so it's best to always post your OS and shell.

Don't unset IFS - reset it to its former (saved!?) value.