tail the output of tail -n 1

raj k yadav · 02-01-2010, 09:00 AM

Hi All,

I want to tail the latest log file in one command line. I dont know what command/option to use for the same.

Please help me. Thanks in advance.

neonsignal · 02-01-2010, 09:08 AM

If you mean that you want to look at the latest log message from any of the /var/log files, then something like:

Code:

tail -n 1 $(ls -t /var/log/ | head -n 1)

(the ls part finds the name of the most recently modified log file)

This won't work with the '-f' (follow) flag for the tail.

raj k yadav · 02-01-2010, 09:28 AM

Thanks for the solution. It works for me but i need to understand a bit more. The way I want to do is:

cd /data/logs/LOG/SIG_SER/Feb-2010-SIG_SER; ls -ltrh| tail -n 1 > $LOGFILE1 | tail -n 20 "echo $LOGFILE1"
-bash: 1: ambiguous redirect
tail: cannot open `echo ' for reading: No such file or directory

Can you please guide me on this.

catkin · 02-01-2010, 09:48 AM

This will corect the error

Code:

cd /data/logs/LOG/SIG_SER/Feb-2010-SIG_SER; ls -ltrh | tail -n 1 > $LOGFILE1 | tail -n 20 "$LOGFILE1"

but this is neater

Code:

cd /data/logs/LOG/SIG_SER/Feb-2010-SIG_SER; ls -ltrh | tail -n 1 | tail -n 20 -

EDIT:

Nonsense! Sorry

This is better

Code:

cd /data/logs/LOG/SIG_SER/Feb-2010-SIG_SER
tail -n 20 "$(ls -ltrh | tail -n 1)"

neonsignal · 02-01-2010, 03:39 PM

Quote:

Originally Posted by raj k yadav

Thanks for the solution. It works for me but i need to understand a bit more. The way I want to do is:

cd /data/logs/LOG/SIG_SER/Feb-2010-SIG_SER; ls -ltrh| tail -n 1 > $LOGFILE1 | tail -n 20 "echo $LOGFILE1"

You are on the right track, but there are several issues.

The quotes aren't quite correct in the last part of your command. To insert the output of a command like echo into another command, you either have to use backquotes, or the $() notation, eg:

Code:

tail -n 20 `echo $LOGFILE1`

Code:

tail -n 20 "$(echo $LOGFILE1)"

However, there is no need to 'echo' a variable, since you can place it directly in the command anyway.

Also, you cannot assign to a variable $LOGFILE by using the redirection. So ultimately your line would end up something like this:

Code:

LOGFILE1=$(ls -tr | tail -n 1); tail -n 20 "$LOGFILE1"

I suspect you are also trying to display the log file details as well. This requires a separate command. The pipe '|' is fine for passing results from one command to the next, but the semicolon ';' is used for running multiple commands on a single line. eg

Code:

LOGFILE1=$(ls -tr | tail -n 1); ls -lh "$LOGFILE1"; tail -n 20 "$LOGFILE1"

raj k yadav · 02-07-2010, 12:26 AM

Thanks to Catkin and Neonsignal. The way u explained is very good. It really worked for me. Thank you so much.