Here’s how to determine the dates when the Daylight Savings Time changes for a given year (I keep forgetting how to do this.):

zdump -v /etc/localtime|grep 2008 /etc/localtime Sun Mar 9 06:59:59 2008 UTC = Sun Mar 9 01:59:59 2008 EST isdst=0 gmtoff=-18000 /etc/localtime Sun Mar 9 07:00:00 2008 UTC = Sun Mar 9 03:00:00 2008 EDT isdst=1 gmtoff=-14400 /etc/localtime Sun Nov 2 05:59:59 2008 UTC = Sun Nov 2 01:59:59 2008 EDT isdst=1 gmtoff=-14400 /etc/localtime Sun Nov 2 06:00:00 2008 UTC = Sun Nov 2 01:00:00 2008 EST isdst=0 gmtoff=-18000

 

Obviously, change 2008 to whatever year you want.

I found this command useful in finding out which top 10 processes are hogging my CPU resources. Note that this command is specific to the Red Hat flavor of Linux. See the man page for ps for the correct output format to use for your specific platform:

ps -eo pcpu,pid,user,args | sort -k1 -r | head -11

Substitue pcpu above with pmem to see the memory hogs instead.

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

 

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'

Line terminations for different operating systems:

unix	0x0a	LF
Classic Mac	0x0d	CR
Windows	0x0d 0x0a	CR LF

To convert a text file with DOS line termination to UNIX line termination:

tr -d '15'  unixfile.txt

or

sed s/.$// winfile.txt > unixfile.txt

To convert a unix file to a DOS file:

sed s/$/x0d/ unixfile.txt > winfile.txt