How can I check if a string is in an array without iterating over the elements?

With bash 4, the closest thing you can do is use associative arrays.

declare -A map
for name in hello world my name is perseus; do
  map["$name"]=1
done

...which does the exact same thing as:

declare -A map=( [hello]=1 [my]=1 [name]=1 [is]=1 [perseus]=1 )

...followed by:

tgt=henry
if [[ ${map["$tgt"]} ]] ; then
  : found
fi

There will always technically be iteration, but it can be relegated to the shell's underlying array code. Shell expansions offer an abstraction that hide the implementation details, and avoid the necessity for an explicit loop within the shell script.

Handling word boundaries for this use case is easier with fgrep, which has a built-in facility for handling whole-word fixed strings. The regular expression match is harder to get right, but the example below works with the provided corpus.

External Grep Process

array=('hello' 'world' 'my' 'name' 'is' 'perseus')
word="world"
if echo "${array[@]}" | fgrep --word-regexp "$word"; then
    : # do something
fi

Bash Regular Expression Test

array=('hello' 'world' 'my' 'name' 'is' 'perseus')
word="world"
if [[ "${array[*]}" =~ (^|[^[:alpha:]])$word([^[:alpha:]]|$) ]]; then
    : # do something
fi


array=('hello' 'world' 'my' 'name' 'is' 'perseus')
regex="^($(IFS=\|; echo "${array[*]}"))$"

test='henry'
[[ $test =~ $regex ]] && echo "found" || echo "not found"

You can use an associative array since you're using Bash 4.

declare -A array=([hello]= [world]= [my]= [name]= [is]= [perseus]=)

test='henry'
if [[ ${array[$test]-X} == ${array[$test]} ]]
then
    do something
else
    something else
fi

The parameter expansion substitutes an "X" if the array element is unset (but doesn't if it's null). By doing that and checking to see if the result is different from the original value, we can tell if the key exists regardless of its value.

Tags:

Bash

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