Sometimes I need to compare two similar files and get to know what entry is in file1, what entry is in file2, I have tried read each file and loop through the files line by line and compare the lines with regex, but it turned out to be very dumb idea and I never got it working. After reading more Perl doc and mailling list, apparently, the perl hash variable is the way to define uniqness of a record, here is the perl script I I got it working:

#!/usr/bin/perl
use strict;
use warnings;
use Tie::File;

tie my @array1, 'Tie::File', "/tmp/u1.txt" or die "Could not tie: $!";

tie my @array2, 'Tie::File', "/tmp/u2.txt" or die "Could not tie: $!";

my %index;
foreach my $entry (@array1) {
if (not exists $index{$entry}) {
$index{$entry} = 1;
}
}

foreach my $entry (@array2) {
if (not exists $index{$entry}) {
$index{$entry} = 2;
}
else {
$index{$entry} += 2;
}
}

foreach my $entry (keys %index) {
if ($index{$entry} == 1) {
print "Entry $entry is only in file one\n";
}
elsif ($index{$entry} == 2) {
print "Entry $entry is only in file two\n";
}
elsif ($index{$entry} == 3) {
print "Entry $entry is in both files\n";
}
else {
print "Entry $entry is screwed up!\n";
}
}

perl -pi'.orig' -e 's/oldstring/newstring/g' fileA, fileB...the i argument is backup option, fileA, fileB will be backed up as fileA.orig, fileB.orig. Ever have format problem with '\r','^M', '\n' after transfering files between windows/mac/linux. try perl -pi'.orig' -e 's/\r(\n)?/\n/g' fileA, fileB...

If on unix/linux, try unix2dos command

Such a simple question, silly me. run tcpdump on both end and specify the src host and dst port or src port.

While fiddling with mysql setup, the new mysql command client connect to the new mysql server fine, but not old mysql command client, so I have to make symbolic link to the new mysql command client like ln -s /usr/local/mysql/bin/mysql /usr/bin/mysql, same as mysqladmin...

I thought the above symbolic link should solve all the setup problem, but it didn't. When I run the WebCalendar setup and test mysql conncetion from the web setup interface, error "could not connect /var/lib/mysql/mysql.sock..." pops up, damn! why would the WebCalendar look for the old mysql server socket file instead of the new one /tmp/mysql.sock? is this PHP mysql client problem? To work around this issue, I reset the socket file to /var/lib/mysql/mysql.sock in the mysql client and server section of /etc/my.cnf "socket = /var/lib/mysql/mysql.sock" and restarted msyqld. this sovled the socket problem.
I was so happy to get rid of the complain and test the mysql connection again, but guess what, I came across another problem "Client does not support authentication protocol". I googled around the Internet, found the http://dev.mysql.com/doc/refman/5.0/en/old-client.html link. (pre-4.1) mysql clients does not support the new hash algorithm, well, I don't know how the WebCalendar PHP application call the old mysql client and don't want to update all mysql client libraries. I could reset the WebCalendar mysql user password to pre-4.1 style:

mysql> SET PASSWORD FOR
-> 'webcalendar'@'localhost' = OLD_PASSWORD('newpwd');

I can identify these accounts with the following query:

mysql> SELECT Host, User, Password FROM mysql.user
-> WHERE LENGTH(Password) > 16;

when you

mysql> desc mysql.user;

you will see the pos-4.1 mysql use varchar(41) to define the "Password" colum.

After I reset the Password, all works fine

Today, I tried to dd if=boot.img of=/dev/fd0 bs=1024 conv=sync; sync , but I always got error message "dd: opening '/dev/fd0', read-only file system". then I fdformatted /dev/fd0 and did the dd command again, it works