github.com/olljanat/moby@v1.13.1/builder/dockerfile/wordsTest (about)

     1  hello | hello
     2  hello${hi}bye | hellobye
     3  ENV hi=hi
     4  hello${hi}bye | hellohibye
     5  ENV space=abc  def
     6  hello${space}bye | helloabc,defbye
     7  hello"${space}"bye | helloabc  defbye
     8  hello "${space}"bye | hello,abc  defbye
     9  ENV leading=  ab c
    10  hello${leading}def | hello,ab,cdef
    11  hello"${leading}" def | hello  ab c,def
    12  hello"${leading}" | hello  ab c
    13  hello${leading} | hello,ab,c
    14  # next line MUST have 3 trailing spaces, don't erase them!
    15  ENV trailing=ab c   
    16  hello${trailing} | helloab,c
    17  hello${trailing}d | helloab,c,d
    18  hello"${trailing}"d | helloab c   d
    19  # next line MUST have 3 trailing spaces, don't erase them!
    20  hel"lo${trailing}" | helloab c   
    21  hello" there  " | hello there  
    22  hello there     | hello,there
    23  hello\ there | hello there
    24  hello" there | hello there
    25  hello\" there | hello",there