In file.name, I have a line that reads

$IDIR/imgen -usemonths -dropcheck -monitor -sizelimit 80000000 -interval 120 -volcal HSI

How can I get the size limit, i.e. 80000000 out and pass it to a variable called SIZE?

Thanks. I tried
echo "grep sizelimit file.name" | sed -n -e 's/^.sizelimit\([0-9]*\) -interval.*$/\1/p'

but it output nothing.

So close...

SIZE=`grep sizelimit myfile | sed 's/^.*sizelimit //' | awk '{print $1}'`

SIZE=0
grep sizelimit myfile | while read s
do
  set -- $s
  while [ $# -gt 0 ]
  do
    case $1 in
      -sizelimit) SIZE=$2; break;;
      *) shift;;
    esac
  done
done

Thanks a lot prowla!
The first option works fine. Did you mean it works even if "-sizelimit 80000000" is moved somewhere else in the line too?

No probs, and yes - the line can change just so long as -sizelimit is followed by its value.
What it actually does is chops everything from the start of the line up to and including the word sizelimit and the space after, and then takes the first word from the remainder (which is the value of sizelimit).