How can I write/create a powershell script verbatim, from another powershell script?

tl;dr:

To create a verbatim multi-line string (i.e., a string with literal contents), use a single-quoted here-string:

$multiLineScript2 = @'

    $startDate2 = (get-date).AddDays($resultOfSubtraction).ToShortDateString();
    $endDate2 = (get-date).AddDays($resultOfSubtraction + 1).ToShortDateString();
'@

Note the use of @' and '@ as the delimiters.

Use a double-quoted here-string only if string expansion (interpolation) is needed; to selectively suppress expansion, escape $ chars. to be included verbatim as `$, as shown in your own answer.

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String Literals in PowerShell

Get-Help about_quoting rules discusses the types of string literals supported by PowerShell:

• To get a string with literal content (no interpolation, what C# would call a verbatim string), use single quotes: '...'

  • To embed ' chars. inside a '...' string, double them (''); all other chars. can be used as-is.

• To get an expandable string (string interpolation), i.e., a string in which variable references (e.g., $var or ${var}) and expressions (e.g., $($var.Name)) can be embedded that are replaced with their values, use double quotes: "..."

  • To selectively suppress expansion, backtick-escape $ chars.; e.g., to prevent $var from being interpolated (expanded to its value) inside a "..." string, use `$var; to embed a literal backtick, use ``
  • For an overview of the rules of string expansion, see this answer.

Both fundamental types are also available as here-strings – in the forms @'<newline>...<newline>'@ and @"<newline>...<newline>"@ respectively (<newline> stands for an actual newline (line break)) – which make defining multi-line strings easier.

• Important:
  • Nothing (except whitespace) must follow the opening delimiter – @' or @" – on the same line – the string’s content must be defined on the following lines.
  • The closing delimiter – '@ or "@ (matching the opening delimiter) – must be at the very start of a line.
  • Here-strings defined in files invariably use the newline format of their enclosing file (CRLF vs. LF), whereas interactively defined ones always use LF only.

Examples:

# Single-quoted: literal:
PS> 'I am $HOME'
I am $HOME

# Double-quoted: expandable
PS> "I am $HOME"
I am C:\Users\jdoe

# Here-strings:

# Literal
PS> @'
I am
  $HOME
'@
I am
  $HOME

# Expandable
PS> @"
I am
  $HOME
"@
I am
  C:\Users\jdoe