Van egy trükk while-nél... így próbáld meg:
while read FS US; do
echo "$FS:$US"
if [ "$US" -gt 5 ]; then
echo "FIRED!"
CRITICALS=$( append "$CRITICALS" "$FS: $US%!!!" )
echo "$CRITICALS"
else
if [ "$US" -gt 85 ]; then
WARNINGS=$( append "$WARNINGS" "$FS: $US%" )
fi
fi
done < <(echo "$FS_PAIRS")