On 1/17/19 1:53 AM, kevin wrote:
>
> Since *[[* isn't a normal command (like [ is), but a /shell
> keyword/, *it has special magical powers*. *It parses its arguments
> before they are expanded by Bash and does the expansion itself*,
> taking the result as a single argument, even if that result contains
> whitespace. (In other words, [[ does not allow word-splitting of its
> arguments.) /However/, be aware that simple strings still have to be
> quoted properly. [[ treats a space outside of quotes as an argument
> separator, just like Bash normally would.
>
> Unfortunately, there is no example that shows how *[[* differs from the
> usual shell operation. I know that the documentation does not indicate the
> particular property of "[[" (features)
Sure it does. The expansions and parsing are covered in the man page
description of `[['. For instance:
"Word splitting and pathname expansion are not performed on the
words between the [[ and ]]; tilde expansion, parameter and
variable expansion, arithmetic expansion, command substitution,
process substitution, and quote removal are performed."
The parsing and expansions that `[[' performs are specified completely.
They are different from the set of word expansions a simple command
like `[' undergoes before it is executed.
, and there has been an adjustment
> based on the operator "==" concerning "=~" but I still do not understand
> why we could not have used the normal shell rules. In your example, a user
> may use single quotes to escape the special meaning of the $ sign "abc'$'".
What are those "normal shell rules?" And how would you have applied them
to specify something that was unspecified before? This discussion began in
mid-2006, maybe go back and look at the bug-bash archives to see what
people were reporting?
Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU [email protected] http://tiswww.cwru.edu/~chet/
