math. operation on empty variables

[Juerg . Oehler]

hi,

i am about to program sh scripts based on xpg4 / posix / bourne-sh.

now i made out a difference in behavior, which i would like to show you.

the script is more then simple:
>>>>>>
if [ "$FORCE" -eq 0 ] ; then
    echo "don't force"
else
    echo "force"
fi
>>>>>>

here are the results:
>/usr/bin/jsh test.sh  #sun's bourne-sh
don't force

>/usr/xpg4/bin/sh test.sh #sun's xpg4 / posix sh
don't force

>/usr/bin/ksh test.sh
don't force

>/usr/local/bin/bash test.sh
test.sh: [: : integer expression expected
force

>/usr/local/bin/bash --posix test.sh
test.sh: [: : integer expression expected
force

questions:
- is there any reason for NOT substitute null values to 0 for integer
expressions?
- would be nice posix sh behave the same? (although posix does not define a
lot)
- why do we get the result force after errormsg?

thx for answer

have fun and a nice day.
george

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