How to monitor a growing log file for specific string and print the line to terminal in realtime?

zhengger

12/1/23, 7:08 AM

For example. I have nohup.out.log file which is growing over time. I want to monitor this file and check if the string test error occurs in this file and print the corresponding lines to terminal or another file such as error.log in real-time. Thanks.

2 + 0

command-line

monitor

log

text-processing

Score:2

Ubuntu

Rinzwind

12/1/23, 7:16 AM

Go to the directory that has nohup.out.log and do...

/usr/bin/tail -f nohup.out.log | grep "test error" > error.log

and it will wait for "test error" to occur.

See man tail for more options.

+ 2

zhengger

12/1/23, 7:42 AM

That's what I need. Thanks!

Raffa

12/4/23, 7:59 AM

Might worth noting as well that `-F` will keep trying to open a file if it is inaccessible as opposed to `-f`.

Score:1

Ubuntu

Artur Meinild

12/1/23, 7:18 AM

lnav is a really good logfile explorer for the terminal that features filtering, syntax highlighting etc.

If you have the universe repo enabled, it can be installed with:

sudo apt install lnav

To use it with a specific logfile, run:

lnav /path/to/nohup.out.log

To set up a filter, press Tab, i. Then type the string test error and hit Enter.

Now only log lines with this string is shown.

+ 1

zhengger

12/1/23, 7:41 AM

A useful tool, though I have no root user. Thanks.

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