file1   file2   file3
1 2 3   1 1 1   3 3 3
2 1 3   1 1 1   3 3 3
0 0 0   1 1 1   3 3 3

1 2 3 1 1 1 3 3 3
2 1 3 1 1 1 3 3 3
0 0 0 1 1 1 3 3 3

paste file1 file2 file3 > file4

1 2 3   1 1 1   3 3 3
2 1 3   1 1 1   3 3 3
0 0 0   1 1 1   3 3 3

paste -d ' ' file1 file2 file3 > file4

-d list     Use one or more of the provided characters to replace the newline characters
             instead of the default tab.  The characters in list are used circularly, i.e., when
             list is exhausted the first character from list is reused.  This continues until a
             line from the last input file (in default operation) or the last line in each file
             (using the -s option) is displayed, at which time paste begins selecting characters
             from the beginning of list again.

             The following special characters can also be used in list:

             n    newline character
             t    tab character
             \    backslash character
                 Empty string (not a null character).

             Any other character preceded by a backslash is equivalent to the character itself.