grep
pesquisa a entrada padrão se nenhum arquivo for fornecido:
grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus (-) is given as file name) for lines containing a match to the given PATTERN. By default, grep prints the matching lines.
Se você acabou de fazer grep doc
grep espera que a entrada padrão venha e pesquise dentro dela (não insira partes entre <
e >
no terminal, estes são comentários):
$ grep doc
a b c <PRESS ENTER HERE>
doc <NO MATCH WAS FOUND IN PREVIOUS LINE, TYPE doc AND PRESS ENTER AGAIN>
doc <MATCH WAS FOUND>