сортировать, объединять или проверять последовательность текстовых файлов (sort, merge, or sequence check text files)
Стандартный вывод сообщений (Stderr)
The standard error shall be used for diagnostic messages. When -c
is specified, if disorder is detected (or if -u is also specified
and a duplicate key is detected), a message shall be written to
the standard error which identifies the input line at which
disorder (or a duplicate key) was detected. A warning message
about correcting an incomplete last line of an input file may be
generated, but need not affect the final exit status.
