Best Practice : Print an array in a bash script

Question

I ran shellcheck on my script and ran into an error on a very simple aspect -

echo "List of fields deleted: ${deleted[@]}"
^-----------^ SC2145: Argument mixes string and array. Use * or separate argument.

I am trying to do similar behavior as below-

declare -a  deleted
deleted = ("some.id.1" "some.id.22" "some.id.333")
echo "List of fields deleted: ${deleted[@]}"

Which is a better practice to print the elements in the array?

echo "List of fields deleted: ${deleted[@]}"

OR

echo "List of fields deleted: "
 for deletedField in "${deleted[@]}"; do echo "${deletedField}"; done

chepner · Accepted Answer · 2019-03-13 19:19:35Z

17

Including a @-indexed array inside a longer string can make for some weird results:

$ arr=(a b c)
$ printf '%s\n' "Hi there ${arr[@]}"
Hi there a
b
c

This happens because the quoted expansion of ${arr[@]} is a series of separate words, which printf will use one at a time. The first word a ends up with Hi there prepended to it (just as anything following the array would be appended to c).

When the array expansion is part of a larger string, you almost certainly want the expansion to be a single word instead.

$ printf '%s\n' "Hi there ${arr[*]}"
Hi there a b c

With echo, it barely matters, as you probably don't care whether echo is receiving one or multiple arguments.

answered Mar 13, 2019 at 19:19

chepner

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