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up vote 2 down vote favorite

Within a bash script, I am building two dynamic arrays. And I want to construct another array with difference of two.

Example:

array1=("aa-1234|safsf|sfsfs" "aa-2345|sfsfs|n0sfm" "aa-0890|ssfsf|sfss" "aa-8097|fsfsf|fsfs" "bb-1234|xvxx|xvxv" "cc-1234|jmsf|sfsfs" "cc-1235|xvxv|xvxv")
array2=(aa-1234 aa-8097)

array1 elements are long entries with | as a delimiter in each.

Now I want to construct an array3, whose elements are all of array1 except those matching in array2.

I tried a for loop to skip through elements. However array1 being a long one, it too much time. I'm looking for a more efficient way.

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1 Answer 1

up vote 2 down vote accepted

I would construct a regular expression out of the 2nd array, and then compare the elements of the 1st array against it:

$ re=$(IFS='|'; echo "^(${array2[*]})\|")
$ echo "$re"
^(aa-1234|aa-8097)\|
$ for elem in "${array1[@]}"; do if [[ $elem =~ $re ]]; then array3+=("$elem"); fi; done
$ printf "%s\n" "${array3[@]}"
aa-1234|safsf|sfsfs
aa-8097|fsfsf|fsfs

If the arrays are much larger than shown, I'd farm the exercise out to grep

$ grep -Ff <(printf "%s\n" "${array2[@]}") <(printf "%s\n" "${array1[@]}")
aa-1234|safsf|sfsfs
aa-8097|fsfsf|fsfs
share|improve this answer
    
Glenn, Thanks for the solution. This works best for Intersection of arrays. However I am looking for entries of array1 excluding matching entries of array2 –  sudobash Nov 21 '14 at 1:20
1  
So just negate it: if ! [[ $elem =~ $re ]] or grep -v -Ff ... –  glenn jackman Nov 21 '14 at 2:43

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