Unix sort treatment of underscore character

Question

I have two linux machines, on which unix sort seems to behave differently. I believe I\'ve narrowed it down to the treatment of the underscore character.

If I run

Answer 1

This is likely caused by a difference in locale. In the en_US.UTF-8 locale, underscores (_) sort after letters and numbers, whereas in the POSIX C locale they sort after uppercase letters and numbers, but before lowercase numbers.

# won't change LC_COLLATE=C after execution
$ LC_COLLATE=C sort filename

You can also use sort --debug to show more information about the sorting behavior in general:

$ (echo 'foo_bar'; echo 'fooAbar'; echo 'foo0bar'; echo 'fooabar') |
      LC_COLLATE=en_US.UTF-8 sort --debug
sort: using ‘en_US.UTF-8’ sorting rules
foo0bar
fooabar
fooAbar
foo_bar

$ (echo 'foo_bar'; echo 'fooAbar'; echo 'foo0bar'; echo 'fooabar') | 
      LC_COLLATE=C sort --debug
sort: using simple byte comparison
foo0bar
fooAbar
foo_bar
fooabar

As also shown in this answer, you can use the above formula to force LC_COLLATE=C for a single command, without modifying your shell environment: