Re: [coreutils] coreutils-7.0 expr exposes long-standing bug in matlab startup script

[Eric Blake]

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According to Martin Knapp-Cordes on 10/22/2008 12:17 PM:
> This means that the MATLAB startup shell script is indeed
> not Open Group compliant. Obviously, no change will be
> necessary to the script if the proposed fixes are approved,
> as they appear to be.
> 
> However, this non-compliance is somewhat of a concern and a
> minimum time frame for a fix has been established, but
> the actual details still need to be worked out.

As pointed out earlier in this thread, and also in
http://www.gnu.org/software/autoconf/manual/autoconf.html#Limitations-of-Usual-Tools,

expr X"$string" : X'regex'

coupled with any necessary postprocessing to account for the leading X,
provides a portable solution for the case when $string starts with -,
across ALL known implementations of expr (whether or not they obey the
POSIX rules to honor --, and whether or not they provide options as
extensions to POSIX).

In the case of numeric analysis, you can use a leading '0 +' to avoid
problems with interpreting a negative number as an option.

And finally, in the particular example that started this thread:

if [ `expr "$lscmd" : '.*->.*'` -ne 0 ]; then
  # do stuff here...
fi

can be rewritten as the following faster alternative (completely avoiding
a fork, and any expr bugs, altogether):

case $lscmd in
  *'->'* ) ;;
  *) # do stuff here...
    ;;
esac

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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