Question

I found an implementation of the associative array here and would like to understand what the code actually does. Here are the piece of the code I don’t understand, and would appreciate the explanation.
‘

put() {
    if [ "$#" != 3 ]; then exit 1; fi  
    mapName=$1; key=$2; value=`echo $3 | sed -e "s/ /:SP:/g"`  #dont understand 
    eval map="\"\$$mapName\""  **#dont understand** 
    map="`echo "$map" | sed -e "s/--$key=[^ ]*//g"` --$key=$value"  #dont understand 
    eval $mapName="\"$map\""  #dont understand 
}
get() {
    mapName=$1; key=$2

    map=${!mapName}
    #dont understand 
    value="$(echo $map |sed -e "s/.*--${key}=\([^ ]*\).*/\1/" -e 's/:SP:/ /g' )"  
}

getKeySet() {
    if [ "$#" != 1 ]; 
    then 
        exit 1; 
    fi

    mapName=$1; 

    eval map="\"\$$mapName\""

    keySet=`
           echo $map | 
           sed -e "s/=[^ ]*//g" -e "s/\([ ]*\)--/\1/g"   #dont understand 
          ` 
}

Thanks.

Answer 1

So first in order of don’t understands:

1. this simply checks you always have 3 arguments to the function and if different number is provided exits with 1(error)
2. This escapes the space chars by replacing them with :SP: so Hi how are you becomes Hi:SP:how:SP:are:SP:you
3. The map is stored in a var with name the first argument provided to put. So this line adds to the var the following text –$key=$value and here key is the second argument and value is the escaped third argument
4. get simply stores in value the value for the key provided as second argument(first one is the name of the map)

To understand better try printing the variable you decided to use for your map after each operation. It’s easy you’ll see 😉
Hope this makes it clear.