pattern matching within two bash arrays

Question

I found quite a few posts on this but couldn't put together the pieces to solve my issue. So say I have two arrays:

array1=( adir bdir anicedir )
array2=( adir anice )

I would like to have a third array like so

array3=( adir anicedir )

More specifically if the first 5 characters of the i-th element in array2 match the first 5 characters of any element in array1 then substitute array2[i] with array1[i]

chepner · Accepted Answer · 2016-12-01 16:37:28Z

2

There's nothing particularly short, because bash isn't a data-processing language. You need to use a loop.

array1=( adir bdir anicedir )
array2=( adir anice )
array3=()

for val2 in "${array2[@]}"; do
    for val1 in "${array1[@]}"; do
        if [[ ${val1:0:5} == "${val2:0:5}" ]]; then
            array3+=("$val1")
            break
        fi
    done
done

Quoting the right-hand side of == ensures that literal string comparison, not pattern matching, is performed.

edited Dec 1, 2016 at 16:37

answered Dec 1, 2016 at 13:56

chepner

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4 Comments

Manfredo Over a year ago

OK, though it still gives me no output. Does echo ${array3[@]} give to you the correct output?

Manfredo Over a year ago

Now I get echo ${array3[@]} adir anice but it should be echo ${array3[@]} adir anicedir. Anyway it already helps, I will try to figure it out. Thanks

chepner Over a year ago

Ah, misread the desired output. Fixed, and in a much simpler manner. Just use substring expansion ${<var>:<star>t:<length>} to compare the 5-character prefix of each array element to each other.

Manfredo Over a year ago

Yeah I think that now it's spot on. Thanks

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