On 9/1/15 5:05 PM, Dennis Williamson wrote: > 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
Because `foo' is expanded, but the value is not treated as an expression. The dash arithmetic evaluator never treats values resulting from expansion as expressions, only as constants. > $ echo $(($foo)) # both expansion and indirection succeed > 5 Because the arithmetic evaluator sees $(( bar )). The word expansion that happens before arithmetic evaluation expands $foo. http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_04 is the Posix specification for arithmetic evaluation. -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, ITS, CWRU c...@case.edu http://cnswww.cns.cwru.edu/~chet/
