Split long output into two columns

column seems to be what you want:

$ cat file
A aldkhasdfljhaf
B klajsdfhalsdfh
C salkjsdjkladdag
D lseuiorlhisnflkc
E sdjklfhnslkdfhn

$ column file
A aldkhasdfljhaf    D lseuiorlhisnflkc
B klajsdfhalsdfh    E sdjklfhnslkdfhn
C salkjsdjkladdag   F kjhnakjshddnaskjdh

To columnate the output, pr converts text files for printing:

-COLUMN, --columns=COLUMN: output COLUMN columns
      and print columns down, unless -a is used.

-t, --omit-header : omit page headers and trailers

e.g.

ls /etc | pr -2 -t
abrt                                gtk-2.0
acpi                                hal
adjtime                             hba.conf
agent.properties                    host.conf
aliases                             hosts
aliases.db                          hosts.allow
...

You can split the file in two (with the same number of lines or the first file having one line more) and then do this:

paste file1 file2

If the length of the lines is too different then is may be necessary to use printf to adapth the lengths by padding with spaces.