grep, print lines matching a pattern
1. Introduction
grep searches the input files
for lines containing a match to a given
pattern list. When it finds a match in a line, it copies the line to standard
output (by default), or does whatever other sort of output you have requested
with options.
Though grep expects to do the matching on text,
it has no limits on input line length other than available memory,
and it can match arbitrary characters within a line.
If the final byte of an input file is not a newline,
grep silently supplies one.
Since newline is also a separator for the list of patterns, there
is no way to match newline characters in a text.
