I stumbled across an old blog post of mine about using grep with more than one expression: in the old days I used -e several times, one for each new expression. But as stressed in the comments that way is neither convenient nor reliable on ll platforms. And I have developed as well, so today I usually use egrep if I need to grep for several expressions. Thus, here are some short notes about using it.
The multiple arguments you are searching for a passed to egrep separated by pipes. For example, if you want to grep the output of lspci for all audio and video controllers, the correct command is:
$ lspci|egrep -i 'audio|vga' 00:05.0 Audio device: NVIDIA Corporation MCP61 High Definition Audio (rev a2) 00:0d.0 VGA compatible controller: NVIDIA Corporation C61 [GeForce 6150SE nForce 430] (rev a2)
( Yes, I know, I write my blog post on pretty old hardware right now 😉 )
egrep does understand more than two expressions, so you can use the option like $STRING_1|$STRING_2|$STRING_3|.... But don’t forget to include the high tics ' in the command: these ensure that the pipe is used as a separator instead of being interpreted by your shell.
/home/liquidat 
If you actually have one of those, then you are quite lucky it hadn’t exploded or melted yet (message from a tx1000-using user)
Whut? Stop scaring me =D
I’m pretty sure I’ve missed out on extended regex several times, but my man page says, “Direct invocation as either egrep or fgrep is deprecated, but is provided to allow historical applications that rely on them to run unmodified.” You might want the capital e switch with grep instead.
PS—Rather, you might enjoy an egrep alias: e.g., alias egrep=’grep -E’ in ~/.bashrc.
Oh well, I never stop learning – however, I guess the alias is the best thing since adding options is waht I want to avoid…
Thanks for pointing it out though. I guess I’ll have to write another short tip in some weeks 😉
liquidat, you could carry your .bashrc around with you too.
egrep is just ‘grep -E’
I’ll one-up you on that, and suggest ‘grep -P’ which gives you even more useful regex features…
You mean Perl regex? Yeah, that can come in handy, you are right…
With ‘ack’ (http://betterthangrep.com) one can simply use Perl regex and it is IMHO way better than grep (for reasons listed on its website), so it replaced grep here completely…
Nice hint – however, I often work on various systems of various customers and have to work with what I find there. Thus ack is only an option for machines which are fully under my control…