Issue running bash script at if statement

I am just getting starting in AppleScript and am testing out an existing script to see if I can get it to run on my computer. The error I get is here:

Expected “,” or “]” but found unknown token.

and it highlights the ~ in my if statement:

path="/Library/Desktop Pictures/Wallpaper-Blue-3D-logolow-2846x1600.jpg"
    
    if [ -d ~/Library/Desktop\ Pictures/ ]
    then
            echo "Desktop Pictures directory already exists"
    else
            mkdir ~/Library/Desktop\ Pictures/
    fi

What am I missing? Thanks!!