Dave Rutherford wrote:
I know test's quirks. Does [[ have quirks? Are they the same?
Is there room in my grey matter to hold both sets of quirks
and keep them straight?
[[ was designed to remedy test's quirks, so it shouldn't really have
any of its own. In addition to the functionality provided by the
new operators and extended matching there is:
1. a more regular grammar, including operator short-circuiting and
better parsing ( [[ -f ]] is an error, for instance; and
[[ -f = ]] doesn't throw an error like the system v test)
2. no word splitting or pathname expansion performed on arguments --
each argument ends up as a single word
3. parameter and variable expansion is more convenient, since [[ is
not a command invoked after all expansions a performed. The intent
is to eliminate the need for excessive quoting: [[ -n $n ]] and
[ -n $n ] behave differently when `n' is unset or null; [ requires
quoting arguments but even that isn't sufficient in all cases
Since [[ was new and had a single specification, the intent was that
users would not have to deal with the portability problems inherent in
the different historical test implementations (Dave Korn implemented it
in the pre-Posix era, remember).
Posix tried to fix some of test's shortcomings within the constraint
of leaving it a builtin command, mostly by defining the behavior based
on the number of arguments and specifying some operator precedence,
but [[ still has its advantages. That means that test is more portable
than [[, of course.
Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
Live Strong. No day but today.
Chet Ramey, ITS, CWRU [EMAIL PROTECTED] http://cnswww.cns.cwru.edu/~chet/
