Send mail with the latest file's content if appended

Question

There is /var/log/httpd/error_log file which contains errors from the whole httpd.

I want to be able to send those new log via email message if any appears - with for example 15 minutes interval. I would like to use CRON to call bash script that will send new content.

Is there any efficience way to obtain, which lines were appended since last check ?

Answer 1

When sending a mail, you can store the line count of the file somewhere (e.g., a file), and then use tail +n to print only from the n-th line on, like

last_linecount=`cat .last_linecount` # or check if file does not exist
wc -l /var/log/httpd/error_log >.last_linecount
tail -n +$((last_linecount + 1)) /var/log/httpd/error_log | whatever

You should also check if the current number of lines is lower than last_linecount, as then the logfile might have been rotated (if applicable) and you have to combine both the tail on the old logfile and everything from the new logfile.

Answer 2

You can use the error_log as a marker and don't need store line numbers in the external file.

the next script:

#!/bin/bash

STRING="last_log_check_point_string"
LOGFILE="/opt/local/apache2/logs/error_log"
URL="http://localhost/$STRING"

linenum=$(grep -n "$STRING" $LOGFILE | tail -1 | sed 's/:.*//')
curl "${URL}" >/dev/null 2>&1
[[ ! -z "$linenum" ]] && sed -n "$linenum,\$p" < $LOGFILE | mail -s "error log at $(date)" "your@email.com" 

• will find the line number of the last occurence of last_log_check_point_string
• will make an request to your web with nonexistent url what contain your string (so, you get an new notice into the error_log - the new marker_point)
• every line after the above line number will mail to you.

The last line of the error_log will be the new marker point, so you have a control how the script works. If you don't have curl, use wget - or is possible make a request with a pure bash too.

or the variant - you will get email only when some errors occured

#!/bin/bash

STRING="last_log_check_point_string"
LOGFILE="/opt/local/apache2/logs/error_log"
URL="http://localhost/$STRING"
TEMPFILE="/tmp/hterror.$$"

linenum=$(grep -n "$STRING" $LOGFILE | tail -1 | sed 's/:.*//')
curl "${URL}" >/dev/null 2>&1
[[ ! -z "$linenum" ]] && sed -n "$linenum,\$p" < $LOGFILE | grep -v "$STRING" >$TEMPFILE
[[ -s "$TEMPFILE" ]] && mail -s "error log at $(date)" "your@email.com"  < $TEMPFILE
rm -f "$TEMPFILE"