filename contains:

123 4
1234 5
12345 689

i want result:
1234
12345
12345679

cat filename | awk '{print $1, $2, $3}' will get my result, but too many $$s.

sed -e 's/[ ]//g' filename will take care one space, [ ] will take 2 spaces.

is it a short way to do this ?