sort(1posix) - sort, merge, or sequence check text files
-c     Check that the single input file is ordered as  specified  by  the  arguments  and  the  collating
       sequence of the current locale. No output shall be produced; only the exit code shall be affected.
-m     Merge only; the input file shall be assumed to be already sorted.
-o  output
       Specify the name of an output file to be used instead of the standard output. This file can be the
       same as one of the input files.
-u     Unique: suppress all but one in each set of lines having equal keys.  If used with the -c  option,
       check  that there are no lines with duplicate keys, in addition to checking that the input file is

The following options shall override the default ordering rules. When ordering options appear independent
of any key field specifications, the requested field ordering rules shall be applied globally to all sort
keys. When attached to a specific key (see -k), the specified ordering options shall override all  global
ordering options for that key.
-d     Specify  that  only  <blank>s  and  alphanumeric  characters,  according to the current setting of
       LC_CTYPE , shall be significant in comparisons. The behavior is undefined for a sort key to  which
       -i or -n also applies.
-f     Consider  all  lowercase  characters  that  have  uppercase  equivalents, according to the current
       setting of LC_CTYPE , to be the uppercase equivalent for the purposes of comparison.
-i     Ignore all characters that are non-printable, according to the current setting of LC_CTYPE .
-n     Restrict the sort key to an initial numeric string,  consisting  of  optional  <blank>s,  optional
       minus  sign, and zero or more digits with an optional radix character and thousands separators (as
       defined in the current locale), which shall be sorted by arithmetic value. An empty  digit  string
       shall be treated as zero.  Leading zeros and signs on zeros shall not affect ordering.
-r     Reverse the sense of comparisons.

The treatment of field separators can be altered using the options:
-b     Ignore  leading  <blank>s  when determining the starting and ending positions of a restricted sort
       key. If the -b option is specified before the first -k option, it  shall  be  applied  to  all  -k
       options.  Otherwise,  the  -b  option  can  be  attached  independently  to each -k field_start or
       field_end option-argument (see below).
-t  char
       Use char as the field separator character; char shall not be considered to  be  part  of  a  field
       (although  it  can  be  included in a sort key). Each occurrence of char shall be significant (for
       example, <char><char> delimits an empty field). If -t is not specified, <blank>s shall be used  as
       default  field separators; each maximal non-empty sequence of <blank>s that follows a non- <blank>
       shall be a field separator.

Sort keys can be specified using the options:
-k  keydef
       The keydef argument is a restricted sort key field definition.  The format of this definition is: