[dos] In MS DOS copying several files to one file

If this is part of a batch script (.bat file) and you have a large list of files, you can use a multi-line ^, and optional /Y flag to suppresses prompting to confirm you want to overwrite an existing destination file.

REM Concatenate several files to one
COPY /Y ^
    this_is_file_1.csv + ^
    this_is_file_2.csv + ^
    this_is_file_3.csv + ^
    this_is_file_4.csv + ^
    this_is_file_5.csv + ^
    this_is_file_6.csv + ^
    this_is_file_7.csv + ^
    this_is_file_8.csv + ^
    this_is_file_9.csv ^
        output_file.csv

This is tidier than performing the command on one line.