How to sort a file, based on its numerical values for a field?

Take a peek at the man page for sort...

   -n, --numeric-sort
          compare according to string numerical value

So here is an example...

sort -n filename

If you are sorting strings that are mixed text & numbers, for example filenames of rolling logs then sorting with sort -n doesn't work as expected:

$ ls |sort -n
output.log.1
output.log.10
output.log.11
output.log.12
output.log.13
output.log.14
output.log.15
output.log.16
output.log.17
output.log.18
output.log.19
output.log.2
output.log.20
output.log.3
output.log.4
output.log.5
output.log.6
output.log.7
output.log.8
output.log.9

In that case option -V does the trick:

$ ls |sort -V
output.log.1
output.log.2
output.log.3
output.log.4
output.log.5
output.log.6
output.log.7
output.log.8
output.log.9
output.log.10
output.log.11
output.log.12
output.log.13
output.log.14
output.log.15
output.log.16
output.log.17
output.log.18
output.log.19
output.log.20

from man page:

   -V, --version-sort
          natural sort of (version) numbers within text