Shell Programming and Scripting

I need to look at a log file every half hour or so to make sure that some activity is going on there. I thought I would write a quick PERL script that would copy the current log file to the temp directory, compare it to the previous log file (from 30 minutes ago) and exit with an error status if the two files are identical. Here is what I threw together.

The log file (for today) is named "log_AutoIndexService_20060501.txt".
It lives in C:\autoindex.
This script will be excuted every thirty minutes, and will page me if it returns an error result code.


=======================
$log_dir = "c:\\autoindex";
$month = substr(`date /T`,4,2);
$year = substr(`date /T`,10,4);
$day = substr(`date /T`,7,2);
$full_date = "$year$month$day";
$file_name = "log_AutoIndexService_$full_date.txt";

`copy $log_dir\\"$file_name" c:\\temp\\AutoIndexService_log.tmp`;

$diff = `fc c:\\temp\\AutoIndexService_log.tmp c:\\temp\\AutoIndexService_log.txt`;

`del c:\\temp\\AutoIndexService_log.txt`;

`ren c:\\temp\\AutoIndexService_log.tmp AutoIndexService_log.txt`;

if( $diff eq "" ) {
exit 1;
}

=======================

So far, the script is running, the files are being copied and removed, but I am not getting paged when the two files are identical. Is my file compare logic wrong, or the way I am using the $diff variable?

Any help would be appreciated.

Backticks returns the standard output of the command executed, not the return value. If the command does not generate any output, it is understandable that a test on $diff is empty.

See perlvar and look for the documentation on $? for a treatment on how to get the return value.