Testing if string values match array elements

Question

I am using a bash script and have a string of comma separated values string="string1,string2,string". There would not be any embedded commas in each string, or spaces. Want to test whether the string elements occur in an array.

What can I do to match string elements with elements of an arbitrary array?

string="element1,element2,element3" array=($(echo $string | tr ',' ' ')) for i in "${array[@]}"; do if [ "$i" == "element2" ]; then echo "element found" fi done 

Answer 1

Maybe you can just do something like:

string=element1,element2,element3 element=element2 case ",$string," in (*,"$element",*) echo element is in string;; (*) echo it is not;; esac 

(standard sh syntax).

To work with arrays or split strings, bash is one the poorest choices of shells.

With zsh, to split a string on a given separator, there's a dedicate operator: the split parameter expansion flag:

array=( "${(@s[,])string}" ) 

(@ and quotes used to preserve empty elements like with the "$@" of the Bourne shell)

To check whether an array has a given element:

if (( $array[(Ie)$element] )); then print element is in the array else print it is not fi 

To split in bash, you can use the split+glob operator (which you did a bit awkwardly with the unquoted $(...)) like in ksh/sh:

IFS=, # split on , instead of the default of SPC/TAB/NL set -o noglob # disable the glob part which you don't want array=( $string'' ) # split+glob; '' added to preserve an empty trailing element # though that means an empty $string is split into one empty # element rather than no element at all 

To lookup array, bash has not dedicated operator either, but you could define a helper function:

is_in() { local _i _needle="$1" local -n _haystack="$2" for _i in "${_haystack[@]}"; do [ "$_i" = "$_needle" ] && return done false } if is_in "$element" array; then echo element is in the array else it is not fi 

Answer 2

You can set up a hashed table of the list of valid words, and then search it (efficiently) for all items in a second list.

#! /bin/bash #.. ./LookUp 04-Feb-2023: Paul_Pedant. declare -A Hash #.. Create at global scope. Setup () { #.. Set up a hash table of the required elements. local j; declare -a q #.. Make the input string into an array like: q=([0]="Monday" ...) IFS=, read -r -a q <<<"${1}" #.. Invert that array like: Hash([Monday]="0" ...) for j in "${!q[@]}"; do Hash+=(["${q[j]}"]="${j}"); done } Query () { #.. Search for words in a list. local s; declare -a q IFS=, read -r -a q <<<"${1}" for s in "${q[@]}"; do if [[ -z "${Hash[${s}]+x}" ]]; then printf '%s is missing\n' "${s}" else printf '%s is index %s\n' "${s}" "${Hash[${s}]}" fi done } Setup "Monday,Tuesday,Wednesday,Thursday,Friday,Saturday,Sunday" Query "Tuesday,BadHairDay,Friday,Holiday,Sunday,Today,Monday,BadDay" 

And the test:

$ ./LookUp Tuesday is index 1 BadHairDay is missing Friday is index 4 Holiday is missing Sunday is index 6 Today is missing Monday is index 0 BadDay is missing $ 

Answer 3

If I understand your question properly, ignoring the bits where you convert the csv to an array, the following can sometimes be used to search for an element within an array however there are caveats when it comes to potential whitespace/newlines, and probably more.

arr=(foo bar baz) if [[ "${arr[*]}" =~ foo ]]; then echo "element found" fi 

Answer 4

I have got the following solution

aggr=("bash" "resource" "rsync") ukeys="resource,rsync" if [[ "${aggr[@]}" =~ $(echo "$ukeys" | tr ',' '|') ]]; then echo "All strings exist in the array." else echo "One or more strings do not exist in the array." fi 

This uses the tr command to replace the commas in the string with pipes, creating a regular expression that can be used with the =~ operator. The $( ... ) syntax is used to run the tr command and capture its output, which is then used as the pattern for the =~ operator. If the regular expression matches any of the elements in the array, the if block will be executed, indicating that all strings in the string exist in the array.

I want to adapt this in a way that if an element in ukeys matches an element in array aggr, then I set display=1.