Patrick O'Callaghan wrote:
> On Mon, 2024-09-09 at 22:32 -0400, Jon LaBadie wrote:
>> Double and single quotes seem equivalent here. But note that inside
>> single quotes the backslash is always literal, not special, while inside
>> double quotes it depends on the character following the backslash. If
>> it is a dollar sign ($), a back tic (`), a backslash (\), or a double
>> quote (") then the backslash quotes the following character.
>
> Many decades of Shell usage and I still have trouble remembering the
> difference between single and double quotes.
Not specifically for you Patrick, but as a general reply to
that statement... (I'm closer to that position than I am to
being an expert in the many, subtle differences, I'm sure.)
A very basic (and very incomplete) way to think about it is
that single quotes protect the contents from (nearly) all
shell expansions (i.e. things which change the content or
meaning of the quoted material). Double quotes allow the
shell to expand things before passing them to the command
being run.
The rules are much more convoluted than that, of course.
Largely, that's by virtue of them being codified by what
shells have actually done rather than being designed
entirely up front before being implemented.
But asking "do I want this data to be fed as-is to the
command being run or expanded by the shell?" usually makes
the choice clear. I tend to default to single quotes and
only change things to double quotes when necessary
By the time you have case where it's not clear, you know
that you're deep in the weeds and likely have looked up the
differences for your use-case (or figured them out through
trial and error).
--
Todd
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