On Tue, Sep 1, 2015 at 3:23 PM, Greg Wooledge <wool...@eeg.ccf.org> wrote:
> On Tue, Sep 01, 2015 at 03:13:57PM -0500, Dennis Williamson wrote: > > The version of dash I have handy (0.5.7) has math support which IMHO is > > broken: > > > > $ foo=bar > > $ bar=5 > > $ echo $foo > > bar > > $ echo $((foo)) > > dash: 4: Illegal number: bar > > $ echo $(($foo)) > > 5 > > $ echo $((bar)) > > 5 > > $ echo $(($bar)) > > 5 > > > > Note the inconsistency in support of omitting the inner dollar sign. > > $foo is expanded to bar, so the following two lines are always going to > be equivalent: > > echo $(($foo)) > echo $((bar)) > It's the line above those two where I demonstrate the failure in the indirection and equivalency. $ echo $((foo)) # expansion succeeds, indirection fails dash: 4: Illegal number: bar $ echo $(($foo)) # both expansion and indirection succeed 5 $ echo $((bar)) # expansion succeeds 5 $ echo $(($bar)) # expansion succeeds 5 Bash doesn't have this inconsistency. (Just don't omit the dollar sign from $RANDOM in most Bourne-derived shells. https://lists.gnu.org/archive/html/bug-bash/2010-01/msg00039.html) > POSIX also specifies (vaguely!!) that $((x)) and $(($x)) are equivalent. > -- Visit serverfault.com to get your system administration questions answered.
