Read properties files in Bash

props.sh

read_props() {
    local key
    if [[ ! -r $1 ]] ; then
        echo file $1 not readable
        exit 1
    fi
    while IFS='=' read -r key value
    do
        if [[ -z ${key} ]] || [[ "${key}" =~ ^# ]] ; then
            continue
        fi
        #key=$(echo $key | tr '.' '_')
        props["$key"]="$value"
    done < "$1"
}

resolve_placeholders() {
    # resolve all placeholders of the form `${PROP}` with the
    # given property `PROP` in `props`.
    for i in "${!props[@]}" ; do
        for placeholder in $(echo -en ${props[$i]} | grep -Po '\${.*?}') ; do
            # remove surrounding ${} from the placeholder
            placeholder=${placeholder#\$\{}
            placeholder=${placeholder%\}}
            props["$i"]=${props[$i]/\$\{$placeholder\}/${props[$placeholder]}}
        done
    done
}

# this is the resulting associative array
declare -A props
# now read all our properties files...
read_props 'src/main/resources/conf/default.properties'
read_props "src/main/resources/conf/prod/application.properties"
# ...and replace all placeholders of the form `my.prop=${my.another.prop}`
resolve_placeholders

# now `props` is filled with all properties from the files and placeholders resolved