Re: [Jython-users] Strange error message when starting Jython

[Ronald F. <yn...@mm...>]

On Tue, Aug 20, 2013, at 7:31, YAMANO Yuji wrote:
> It comes from the jython bash script, not python code. You might want to 
> add -x to the beginning of the line in ~/jython2.5.4rc1/jython to see 
> what's happening.
> 
> On Wed, 07 Aug 2013 19:23:32 +0200, Ronald Fischer <yn...@mm...> wrote:
> > expr: syntax error
> > Jython 2.5.4rc1 (2.5:723492dbab02, Feb 8 2013, 09:50:55) 
> > Any idea where this syntax error comes from?

Thanks for the hint. I researched it and found that it was indeed a bug
in the bash script. There is a line saying:

       if expr "$link" : '/' > /dev/null; then

and this indeed yields a syntax error. The reason is a somewhat arcane
restriction of the "expr" command. From its man-page:

'The expr utility makes no lexical distinction between arguments which
may be operators and arguments which may be operands.  An operand which
is lexically identical to an operator will be considered a syntax
error.'

Indeed, after changing this line to

       if expr "$link" : '[/]' > /dev/null; then

no error anymore. 

It is interesting, that this restriction to 'expr' doesn't seem to be
published widely. The expr man page of MacOSX 10.4 (which I am using)
doesn't mention it, but the documentation for Darwin explain it here:

  https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/expr.1.html

It is documented in the BSD documentation (which, AFIK, is where Mac OSX
is derived from), but the expr found on Linux doesn't have it. This is
probably the reason why the bug got unnoticed for long time.
-- 
Ronald Fischer <ro...@em...>
+  If a packet hits a pocket on a socket on a port, 
+  and the bus is interrupted and the interrupt's not caught,
+  then the socket packet pocket has an error to report.
+		(cited after Peter van der Linden)