On Mon, Apr 2, 2018 at 5:16 PM, PRussell <prusselltechgr...@gmail.com> wrote:
> > echo 4B > ( set -x;var=5;var1=var; (( var1 == $var2 )) && echo yes || echo no ) > > > It appears that 3A and 4A evaluate to 0 because of the arithmetic context. > 3A echo's yes; 4A echo's no. > > The problem is what is happening with 3B and 4B. I tested on bash 4.3.11 > and > bash 4.4.19 and got a slightly different error message. > > Bash version 4.3.11: > > ./tt: line 18: var1: var1 == : syntax error: operand expected (error > token is "== ") > > Bash version 4.4.19 (???? was garabage): > > ./tt: line 18: ????: var1 == : syntax error: operand expected (error > token is "== ") > > Peggy Russell > > The problem here is quite simple. When using "$", the parameter is expanded first. Since it's empty, it expands to the empty string, and the (( keyword simply sees (( var1 == )), which is absolutely a syntax error. When not using "$", no expansions happen before the (( keyword sees the variable name, and so it uses the name correctly. So the fix here is simple: provide variable names without using "$" in an arithmetic context.
