Searching multiple arrays for values and returning the array name

Question

I have an requirement wherein I have multiple values in a file and 8 arrays containing numeric values. For example:

Array1=(1 2 3 4 5) 
Array2=(6 7 8 9 10) 

File has values 3 and 9. So it should return Array1 in first case and Array2 in second case. Also I want to store the result in another file having value followed by array name that contains that value.

Unable to find any solution.

Answer 1

If your bash is recent enough:

for a in Array1 Array2; do
  declare -n arr="$a"
  grep -oFf <(printf '%s\n' "${arr[@]}") file && printf '(in %s)\n' "$a"
done > results

Explanation:

• declare -n arr="$a" declares a nameref, a kind of alias. If executed when the value of a is Array1, arr becomes a synonym of Array1.
• printf '%s\n' "${arr[@]}" prints each entry in array arr on a separate line.
• <(command) is a process substitution, the command is run and its output is seen as a file by the environment. In our case the content of the array is considered as a file with one entry per line.
• grep -oFf file1 file2 takes the patterns to search in file1 (-f file1), in our case in the process substitution, considers them as plain text strings, not regular expressions (-F), and outputs only the matched parts (-o).
• grep exits with status 0 if a pattern matched, else it exits with a non-zero status. As the 0 exit status is considered as boolean true, the printf '(in %s)\n' that prints the array name is executed only if grep found one of the patterns in file, thanks to the && operator (AND).

Demo (output prefixed with -| ):

printf '3\n9\n15\n' > file
Array1=(1 2 3 4 5)
Array2=(6 7 8 9 10)
Array3=(a b c d e)
for a in Array1 Array2 Array3; do
  declare -n arr="$a"
  grep -oFf <(printf '%s\n' "${arr[@]}") file && printf '(in %s)\n' "$a"
done > results
cat results
-| 3
-| 1
-| 5
-| (in Array1)
-| 9
-| (in Array2)

Answer 2

Try this Shellcheck-clean pure Bash code:

#! /bin/bash -p

Array1=(1 2 3 4 5) 
Array2=(6 7 8 9 10) 

while read -r val || [[ -n $val ]]; do
    for arr in Array1 Array2; do
        aref="${arr}[@]"
        for elem in "${!aref}"; do
            if [[ $elem == "$val" ]]; then
                printf '%s %s\n' "$val" "$arr"
                break
            fi
        done
    done
done <file

• This should work on any non-ancient version of Bash. (I tested it with Bash 3.2 (released in 2006).)
• The || [[ -n $val ]] is to support input files that don't have the last line properly terminated. See the My text files are broken! They lack their final newlines! section of BashFAQ/001 (How can I read a file (data stream, variable) line-by-line (and/or field-by-field)?).
• See What does "${!var}" mean in shell script? for an explanation of ${!aref}.
• echo doesn't work reliably for variable data so I used printf to produce the output. See the accepted, and excellent, answer to Why is printf better than echo?.