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-   -   "cat" only the last line. how? (https://www.linuxquestions.org/questions/programming-9/cat-only-the-last-line-how-702728/)

andrew22 02-06-2009 08:24 AM
"cat" only the last line. how?
 
I want to check a log into terminal, the logger writes a temperature_log in /var/log . How can I <<cat>> only the last line of the log, so I can append it to the output?
Here is the bad code:
Code:
#! /bin/bash

cd /var/log
x=0
until [ x = 1 ]; do
echo "`cat temperature_log`" #Thats the bad section
sleep 5
done
echo "Error!"
I wanted to do sommething like this:
Code:
echo "`cat_last_line temperature_log`"
But unfortunately , "cat_last_line" is yet to be invented,
any suggestions?
Edit: the logger updates the log every 5 seconds , thats the "sleep 5" for.

JulianTosh 02-06-2009 08:27 AM
tail -1 temperature_log

jqbsx 02-06-2009 08:29 AM
use: tail -n XX file

andrew22 02-06-2009 08:39 AM
5 minutes and 2 answers , thanks a lot.
Thats the new script:
Code:
#! /bin/bash

cd /var/log
x=0
tail -100 temperature_log #Makes it more flexible and fast than "cat"
until [ x = 1 ]; do
tail -1 temperature_log #Thats the whole deal!!!
sleep 5
done
echo "Error"

JulianTosh 02-06-2009 08:41 AM
slow night at work! ;)

ntubski 02-06-2009 03:08 PM
I think this script might equivalent to
Code:
tail -f /var/log/temperature_log
Code:
~$ man tail
...
      -f, --follow[={name|descriptor}]
              output appended data as the file grows;

JulianTosh 02-06-2009 03:58 PM
Quote:
Originally Posted by ntubski (Post 3434523)
I think this script might equivalent to
Code:
tail -f /var/log/temperature_log
Code:
~$ man tail
...
      -f, --follow[={name|descriptor}]
              output appended data as the file grows;
Not if andrew wants to check the log file every 5 seconds... The -f will not release the script until the user hits ctrl-c. "tail -1" simply outputs the last line of the file and quits so the rest of the script can do it's thing, including "sleep".

shyamkumar1986 02-07-2009 06:00 AM
In that case - you might want to do tail -f 1 "file_name" & instead

chrism01 02-08-2009 05:56 PM
Re post #4
Code:
until [ x = 1 ]; do
tail -1 temperature_log #Thats the whole deal!!!
sleep 5
done
is an infinite loop, so it does look like 'tail -f ...'

syg00 02-08-2009 06:14 PM
Doesn't keep the file open ...


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