Check if a variable exists in a list in Bash

Question

[[ $list =~ (^|[[:space:]])$x($|[[:space:]]) ]] && echo 'yes' || echo 'no'

or create a function:

contains() {
    [[ $1 =~ (^|[[:space:]])$2($|[[:space:]]) ]] && exit(0) || exit(1)
}

to use it:

contains aList anItem
echo $? # 0： match, 1: failed

how about

echo $list | grep -w -q $x

you could either check the output or $? of above line to make the decision.

grep -w checks on whole word patterns. Adding -q prevents echoing the list.

Matvey is right, but you should quote $x and consider any kind of "spaces" (e.g. new line) with

[[ $list =~ (^|[[:space:]])"$x"($|[[:space:]]) ]] && echo 'yes' || echo 'no' 

so, i.e.

# list_include_item "10 11 12" "2"
function list_include_item {
  local list="$1"
  local item="$2"
  if [[ $list =~ (^|[[:space:]])"$item"($|[[:space:]]) ]] ; then
    # yes, list include item
    result=0
  else
    result=1
  fi
  return $result
}

end then

`list_include_item "10 11 12" "12"`  && echo "yes" || echo "no"

or

if `list_include_item "10 11 12" "1"` ; then
  echo "yes"
else 
  echo "no"
fi

Note that you must use "" in case of variables:

`list_include_item "$my_list" "$my_item"`  && echo "yes" || echo "no"

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)

You can use (* wildcards) outside a case statement, too, if you use double brackets:

string='My string';

if [[ $string == *My* ]]
then
echo "It's there!";
fi

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.