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zshassociative-array

Find key that matches value in zsh associative array?

In a regular array, I can use (i) or (I) to search for the index of entries matching a given value (first match from the start or end of the array, respectively):

list=(foo bar baz)
echo $list[(i)bar]
# => 2

This doesn't work for associative arrays, to get (one of) the key(s) where a value is found:

declare -A hash=([foo]=bar [baz]=zoo)
echo $hash[(i)bar]
# => no output

Is there another mechanism for doing this, other than manually looping through?

Solution

  • The (r) subscript flag combined with the (k) parameter flag should give you what you want:

    declare -A hash=([foo]=bar [baz]=zoo)
echo ${(k)hash[(r)bar]}
# => foo

    The man page section on the (r) subscript flag only talks about returning values and ignores this usage, so it's hard to find.