Detect if variable is an array

$ v=(foo bar) # v is an array

$ declare -p v | grep -q '^declare \-a' && echo array || echo no array
array

$ v='declare -a' # v is a string

$ declare -p v | grep -q '^declare \-a' && echo array || echo no array
no array

$ declare -p non-existing-var | grep -q '^declare \-a' && echo array || echo no array
bash: declare: non-existing-var: not found
no array

$ # The `2> dev/null' protects against the `declare: not found' error message above

$ declare -p non-existing-var 2> /dev/null | grep -q '^declare \-a' && echo array || echo no array
 no array

Cited from http://www.fvue.nl/wiki/Bash:_Detect_if_variable_is_an_array