extract data from log using awk and tr

extract_log.sh

#!/bin/sh -

JOB_DIR=$1
NUM=$2
UNCOMP=0

for TASK in `ls $JOB_DIR | grep 'attempt.*_m_.*'`
do
   ucp=`awk '/.*[\[]MapOutputCollector::mid_spill[\]].*/ { print $28 }' $JOB_DIR/$TASK/stderr | tr -cd [:digit:]`
   let "UNCOMP += ucp"
done
let " OUTPUT = $UNCOMP / $NUM / (1024 * 1024) "
echo $OUTPUT MB