you can also combine multiple targets in one command. for example, i
run the following in a screen session on all of my mail servers:
tail -f /var/log/mail/info |grep -v -e pop3d -e imap
the -v is a reverse grep, it returns everything -except- lines that
match the target. i don't care about seeing each user that retreives
their mail via pop or imap, i just want to see smtp messages.
jason
Brian Daniels wrote:
Maybe this one is common knowledge, but it caught me off guard. And it might
save somebody some time.
Assume we have a logfile. To watch it on your terminal, you
could type 'tail -f logfile'.
To filter the output, you could use 'tail -f logfile | grep foo'.
All as expected. But you want more filtering, so you type:
'tail -f logfile | grep foo | grep bar'
And get no output at all, even though there are log entries that contain both
foo and bar!
It turns out that a pipe has a buffer of 4096 characters and is holding the
data. To make it work, you need:
'tail -f logfile | grep --line-buffer foo | grep bar'
and now you get the filtered output as expected.
--Brian
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