Browsing AuthorCelso

August 28, 2007

Bourne Shell Logging Routine

Here’s another logging routine, this one is written in Bourne shell:

#!/bin/sh

log_message() {
    echo `date "+%m/%d/%y %H:%M:%S %Z"` "$1" | tee -a aaa.out
}

log_message "Hello there"
log_message "Goodbye"

Sample output:

08/28/07 23:16:13 EDT Hello there
08/28/07 23:16:13 EDT Goodbye

 

August 23, 2006

Setting MySQL Password

To set up root password the first time:

$ mysqladmin -u root password NeWPasSwORd

To change an existing root password:

$ mysqladmin -u root -p oldpassword newpass
Enter password:

To change a normal user password:

$ mysqladmin -u dbuser-p oldpassword newpass

July 13, 2006

Sorting IP Addresses

The following will sort an array of IP addresses in @in and the sorted IP addresses will be in @out.

@out = sort {
    pack('C4' => $a =~ /(d+).(d+).(d+).(d+)/)
    cmp
    pack('C4' => $b =~ /(d+).(d+).(d+).(d+)/)
} @in;

What this does is it forms a string of four bytes out the IP address octet using the pack() function then sorts it lexicographically.

See also Sorting Section Numbers

June 7, 2006

Determining the External IP Address

Here’s how to find out your external IP address courtesy of this hint:

http://www.macosxhints.com/article.php?story=20060602180942480


curl --silent http://checkip.dyndns.org
    | awk '{print $6}' | cut -f 1 -d "<"

If you are using Apple’s Airport Extreme Basestation (mine is particularly the Time Capsule and this is where I have tested this), and you have the SNMP interface enabled, you can run the following command


prompt$ snmpwalk -Os -c public -v 1 192.168.63.1 ipAdEntAddr IpAddress 
    | grep -E -v '(127.0.0|169.254|192.168.63.1)' 
    | cut -d : -f 2 | sed 's/ //g'

May 24, 2006

Write a Daemon in Perl

The code below is a template for a daemon written in Perl. Use the code below as a starting point when you have to write a program that has to persist in the background to do its things and without a gui.


use POSIX qw(setsid);

chdir '/' or die "Can't chdir to /: $!";
umask 0;
open STDIN, '/dev/null'
    or die "Can't read /dev/null: $!";

#open STDOUT, '>/dev/null'
#    or die "Can't write to /dev/null: $!";

open STDERR, '>/dev/null'
    or die "Can't write to /dev/null: $!";

defined(my $pid = fork)
    or die "Can't fork: $!";

exit if $pid;

setsid or die "Can't start a new session: $!";

while(1) {
    sleep(5);
    print "Hello...n";
}

Note that one of the lines above is commented out to let the output print to the screen. Uncomment this in the final code to silence your program. For more on this code, see this tutorial: http://www.webreference.com/perl/tutorial/9/.