Using OR in grep.

Benedict_White · 2005-10-25 10:42:12

Hi.

i am having some trouble locating a way to do what I want.

I want to tail and follow a log file, which is easy, just tail -f /somelogfile.

Then rather than see the whole lot I want to pick bits out, for example if it was a BB2 and I want to just see posts I could do:

tail -f /some-log-file | grep some-entry

would produce what I want. However, what I want to see is lines that contain either some-entry, or some-other-entry or another-entry

So that I can pick out several types of interesting traffic with out having to have dozens of screens open.

Any one help? The man file implies I can do:

tail -f /some-log-file | grep some-entry |; some-other-entry |; a-third-entry

but this falls down with this bash error:
-bash: syntax error near unexpected token `;'

lanrat · 2005-10-25 11:06:08

If you use "|" don't use ";". But that's the other thing. For grep you can use something like this:

tail -F /some/path/some_file | grep "first-entry|second-entry|some other entry"

Benedict_White · 2005-10-25 11:15:51

Yep, that works.

many thanks. I do like the power of the CLI, and the tools available to manipulate large files for interesting things without having to read the lot.

Many thanks for that.

T-Dawg · 2005-10-25 11:20:00

grep [first-entry,second-entry,some other entry]
should work, the "," are like or's inside "[" brackets.

Benedict_White · 2005-10-25 14:27:19

For some reason that seems to confuse grep and I get the whole tail.

I also tried with
tail -f /some-log-file | grep ['first-entry','second-entry','some other entry']

and that produced the same result.

Benedict_White · 2005-10-25 14:47:09

lanrat's option seems to work well, but what I would like to do now is to pipe the output to another logfile so I tried something like this:

tail -f /some_log_file | grep "first_expression|second_expression|third_expression" > /some_other_logfile

but tailing that shows nothing at all.

Any thoughts?

cactus · 2005-10-25 23:49:31

tail -f /some_log_file | grep -e "first_expression|second_expression|third_expression" > /some_other_logfile

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