is one of Unix’s most useful tools. As
a result, all users seem to want their own, slightly different version that
solves a different piece of the problem. (Maybe this is a problem in itself;
there really should be only one grep, as
the manpage says.) Three versions of grep
come with every Unix system; in addition, there are six or seven freely
available versions that we’ll mention here, as well as probably dozens of
others that you can find kicking around the Net.
Here are the different versions of grep
and what they offer. We’ll start with the standard versions:
Great for searching with regular expressions (Section 13.2).
grep (or egrep)
Handles extended regular expressions.
It is also, arguably, the fastest of the standard greps (Section 13.4).
grep (or fgrep)
So named because it matches fixed
strings. It is sometimes inaccurately called “fast grep“; often it is really the
slowest of them all. It is useful to search for patterns with
literal backslashes, asterisks, and so on that you’d otherwise
have to escape somehow. fgrep
has the interesting ability to search for multiple strings
Of course, on many modern Unixes all three are the same executable, just
with slightly different behaviors, and so you may not see dramatic speed
differences between them. Now for the freeware versions:
agrep, or “approximate grep"
A tool that finds lines that “more or less” match ...
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