Checking that a decimal number is in a range in bc

Question

I've written this if, that is obviously not working, and I still can't manage to get over it:

#LASTEFFECTIVEHASH
if (( $(echo "$LASTEFFECTIVEHASHMINVAL < $LASTEFFECTIVEHASH < $LASTEFFECTIVEHASHMAXVAL" | $BC -l) )); then
                echo "$DATESTAMP - LASTEFFECTIVEHASH=$LASTEFFECTIVEHASH is between $LASTEFFECTIVEHASHMINVAL and $LASTEFFECTIVEHASHMAXVAL"|tee -a $LOGFILE
else
                echo "$DATESTAMP - LASTEFFECTIVEHASH=$LASTEFFECTIVEHASH is not between $LASTEFFECTIVEHASHMINVAL and $LASTEFFECTIVEHASHMAXVAL"|tee -a $MSGFILE $LOGFILE
fi

But, when value are out of ranges, it results in this:

20170810003646 - LASTEFFECTIVEHASH=139.2 is between 104.9 and 136.9

I'm following the maths syntax: if x > 104.9 and < 136.9, in maths you write it 104.9 < x < 136.9. But I suspect that bash/bc are behaving differently from my math's teacher.

It would be great if bc won't fail to count up to 137 ;)

Answer 1

Unlike for example python, bc does not support chained comparisons:

a < b < c

To perform both comparisons and require both to be true, use logical-and (requires GNU bc):

(a < b) && (b < c)

For example:

$ a=104.9; b=136; c=136.9; if echo "($a < $b) && ($b < $c)" | bc -l | grep -q 1; then echo True; else echo False; fi
True
$ a=104.9; b=137; c=136.9; if echo "($a < $b) && ($b < $c)" | bc -l | grep -q 1; then echo True; else echo False; fi
False

POSIX bc

If you don't have GNU bc, you can replace logical-and with multiplication:

$ a=104.9; b=136; c=136.9; if echo "($a < $b)*($b < $c)" | bc -l | grep -q 1; then echo True; else echo False; fi
True
$ a=104.9; b=137; c=136.9; if echo "($a < $b)*($b < $c)" | bc -l | grep -q 1; then echo True; else echo False; fi
False