calculation in a bash script

Haven't been scripting under unix for a long time... many years
Can someone remind me how to calculate 2 + 3 and store the result in a variable.
Must be something with eval and/or bc, but can't find what it is anymore
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JulieBouillonConnect With a Mentor Commented:

echo $SUM
lesouefAuthor Commented:
works. just wondering why we need double (())...

another point if I wanna check if $sum < 10, what's the right syntax? if I use <, it looks for a file to redirect. if I use LEQ, it does not understand...
since i've been javascript, it has confused me more! and the man is really on outdated tool. so am I probably!
You need $(()) because using $(command) is the same as using `command`

$sum < 10
$sum -lt 10

Just a few more operators:
lt -> less than
gt -> greater than
eq -> equal
ne -> equal
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lesouefAuthor Commented:
strange, this was I had done in between.
when using
 if [ $sum < 10 ] ; then etc....
I get in insult something like file not found (10)??
It should have beem more explicit:
it is not -> $sum < 10
but -> $sum -lt 10
lesouefAuthor Commented:
ok, works. many thanks.
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