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Use [[ ${foo[key]:+exists} ]] in Bash for Map Keys

Sometimes you want to check if an associative array has ever had a key defined — even if the value is empty. Use the parameter expansion ‘if unset or null’ notation allows for this when combined with bash double-bracket conditions.

#!/bin/bash

declare -A map
map[foo]=FOO
map[bar]=BAR
map[empty]=

for key in foo bar empty other; do
  [[ ${map[$key]:+exists} ]] && echo "$key exists"
done

Related:

• Bash Manual (man) Page - Parameter Expansion

Tags:

#bash #tips #maps #dicts #associative #arrays

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