shell adding string to an array

Question

I am having some trouble adding a string to an array within a loop. For some reason it always adds the same line. Here is my code:

declare -a properties
counter=0

while read line
do

    if [[ ${line} == *=* ]]
    then
        properties[${counter}]=${line}
        (( counter=counter + 1 ))
    fi
done < ${FILE}

for x in ${!properties[@]}
do
    echo "the value is $properties[x]"
done

For some reason each element in the array is the first line in the file. I must be doing something wrong, just not sure what.

Any help would be greatly appreciated

Solution 1

Try this script:

declare -a properties
while read line
do
   [[ "${line}" == *=* ]] && properties+=("$line")
done < "${FILE}"

for x in "${properties[@]}"
do
   echo "the value is "$x"
done

Solution 2

As @twalberg mentions in this comment, the problem is not in the top loop, but in the bottom one:

for x in ${!properties[@]}
do
    echo "the value is $properties[x]"
done

Array references always need braces { ... } to expand properly.

For some reason each element in the array is the first line in the file.

Not so. The array is correctly populated, but you need to change the reference to the array from:

echo "the value is $properties[x]"

to:

echo "the value is ${properties[x]}"

Just a simple oversight.

Comments

[mklement0]

Your recommendation for building the array is helpful, but please consider removing the rest of your answer: Not only is (( counter=counter + 1 )) correct (albeit clumsy), your alternatives are not an improvement and in the case of counter+=1 incorrect. If anything, (( ++counter )) is the most concise form to use.

[mklement0]

Great improvement, but please double-quote ${properties[@]} to prevent unwanted shell expansions.

[Henk Langeveld]

This eliminates the bug in the original script by looping x over the expanded values, instead of the index. The changes in the upper loop detract from the original bug.

[Henk Langeveld]

Correct, but does not answer the question. And then, you missed an option: [[ ${line} == *=* ]] && properties[counter++]=${line} :-)

[mklement0]

+1 for explaining the problem and showing me that variable references in array subscripts need not be $-prefixed ([x] vs. [$x]) (and that subscripts can even be arithmetic expressions).