Очень полезная штука для анализа логов через grep.
Выводит N строк до совпадения, N строк после:

       -A NUM, --after-context=NUM
              Print NUM lines  of  trailing  context  after  matching  lines.
              Places  a  line  containing  --  between  contiguous  groups of
              matches.

       -B NUM, --before-context=NUM
              Print  NUM  lines  of  leading  context  before matching lines.
              Places a  line  containing  --  between  contiguous  groups  of
              matches.