This is a contrived sample. It sorts records based on an ALPHABET that has upper and lower case characters together, with A and a swapped compared to the other letters. This was done on purpose to demonstrate the possibilities. The SORT algorithm reader retrieves records using RELEASE in the INPUT PROCEDURE. The OUTPUT PROCEDURE uses RETURN for the SORT algorithm writer.

GCobol >>SOURCE FORMAT IS FIXED
      ******************************************************************
      * Purpose:   A GnuCOBOL SORT verb example
      * Tectonics: cobc -x sorting.cob
      *     ./sorting <input >output
      *   or simply
      *     ./sorting
      *   for keyboard and screen demos
      ******************************************************************
       identification division.
       program-id. sorting.

       environment division.
       configuration section.
      * This sets up a sort order lower/upper except for "A" and "a"
       special-names.
           alphabet mixed is " AabBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTu
      -"UvVwWxXyYzZ0123456789".

       input-output section.
       file-control.
           select sort-in
               assign keyboard
               organization is line sequential.
           select sort-out
               assign display
               organization is line sequential.
           select sort-work
               assign "sortwork".

       data division.
       file section.
       fd sort-in.
          01 in-rec        pic x(255).
       fd sort-out.
          01 out-rec       pic x(255).
       sd sort-work.
          01 work-rec      pic x(255).

       working-storage section.
       01 loop-flag        pic x value low-value.

       procedure division.
       sort sort-work
           on descending key work-rec
           collating sequence is mixed
           input procedure is sort-transform
           output procedure is output-uppercase.

       display sort-return.
       goback.

      ******************************************************************
       sort-transform.
       move low-value to loop-flag
       open input sort-in
       read sort-in
           at end move high-value to loop-flag
       end-read
       perform
           until loop-flag = high-value
               move in-rec to work-rec
               RELEASE work-rec
               read sort-in
                   at end move high-value to loop-flag
               end-read
       end-perform
       close sort-in
       .

      ******************************************************************
       output-uppercase.
       move low-value to loop-flag
       open output sort-out
       return sort-work
           at end move high-value to loop-flag
       end-return
       perform
           until loop-flag = high-value
               move work-rec to out-rec
               write out-rec end-write
               return sort-work
                   at end move high-value to loop-flag
               end-return
       end-perform
       close sort-out
       .

       exit program.
       end program sorting.