Check if a variable exists in a list in Bash

Question

I am trying to write a script in bash that check the validity of a user input.
I want to match the input (say variable x) to a list of valid values.

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Answer 1

If your list of values is to be hard-coded in the script, it's fairly simple to test using case. Here's a short example, which you can adapt to your requirements:

for item in $list
do
    case "$x" in
      item1|item2)
        echo "In the list"
        ;;
      not_an_item)
        echo "Error" >&2
        exit 1
        ;;
    esac
done

If the list is an array variable at runtime, one of the other answers is probably a better fit.

Answer 2

Examples

$ in_list super test me out
NO

$ in_list "super dude" test me out
NO

$ in_list "super dude" test me "super dude"
YES

# How to use in another script
if [ $(in_list $1 OPTION1 OPTION2) == "NO" ]
then
  echo "UNKNOWN type for param 1: Should be OPTION1 or OPTION2"
  exit;
fi

in_list

function show_help()
{
  IT=$(CAT <<EOF

  usage: SEARCH_FOR {ITEM1} {ITEM2} {ITEM3} ...

  e.g. 

  a b c d                    -> NO
  a b a d                    -> YES
  "test me" how "test me"    -> YES

  )
  echo "$IT"
  exit
}

if [ "$1" == "help" ]
then
  show_help
fi

if [ "$#" -eq 0 ]; then
  show_help
fi

SEARCH_FOR=$1
shift;

for ITEM in "$@"
do
  if [ "$SEARCH_FOR" == "$ITEM" ]
  then
    echo "YES"
    exit;
  fi
done

echo "NO"

Answer 3

If it isn't too long; you can just string them between equality along a logical OR comparison like so.

if [ $ITEM == "item1" -o $ITEM == "item2" -o $ITEM == "item3" ]; then
    echo In the list
fi 

I had this exact problem and while the above is ugly it is more obvious what is going on than the other generalized solutions.

Answer 4

IMHO easiest solution is to prepend and append the original string with a space and check against a regex with [[ ]]

haystack='foo bar'
needle='bar'

if [[ " $haystack " =~ .*\ $needle\ .* ]]; then
    ...
fi

this will not be false positive on values with values containing the needle as a substring, e.g. with a haystack foo barbaz.

(The concept is shamelessly stolen form JQuery's hasClass()-Method)

Answer 5

I find it's easier to use the form echo $LIST | xargs -n1 echo | grep $VALUE as illustrated below:

LIST="ITEM1 ITEM2"
VALUE="ITEM1"
if [ -n "`echo $LIST | xargs -n1 echo | grep -e \"^$VALUE`$\" ]; then
    ...
fi

This works for a space-separated list, but you could adapt it to any other delimiter (like :) by doing the following:

LIST="ITEM1:ITEM2"
VALUE="ITEM1"
if [ -n "`echo $LIST | sed 's|:|\\n|g' | grep -e \"^$VALUE`$\"`" ]; then
   ...
fi

Note that the " are required for the test to work.

Answer 6

Thought I'd add my solution to the list.

# Checks if element "$1" is in array "$2"
# @NOTE:
#   Be sure that array is passed in the form:
#       "${ARR[@]}"
elementIn () {
    # shopt -s nocasematch # Can be useful to disable case-matching
    local e
    for e in "${@:2}"; do [[ "$e" == "$1" ]] && return 0; done
    return 1
}

# Usage:
list=(11 22 33)
item=22

if elementIn "$item" "${list[@]}"; then
    echo TRUE;
else
    echo FALSE
fi
# TRUE

item=44
elementIn $item "${list[@]}" && echo TRUE || echo FALSE
# FALSE