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Get My Public IP Address

find all active IP addresses in a network
You send a unicast ICMP packet to each host. Many firewalls will drop that ICMP. However, in order to send the ICMP, you'll have first done an ARP request and the remote machine is unlikely to ignore that, so the computer will be in your ARP table.

Select and Edit a File in the Current Directory
This command displays a simple menu of file names in the current directory. After the user made a choice, the command invokes the default editor to edit that file. * Without the break statement, the select command will loop forever * Setting the PS3 prompt is optional * If the user types an invalid choice (such as the letter q), then the variable $f will become an empty string. * For more information, look up the bash's select command

list files in mtime order
Simple but useful; list files in the current directory in mtime order. Useful if you've been working on something and then take a day or two off.

Convert seconds to [DD:][HH:]MM:SS
Converts any number of seconds into days, hours, minutes and seconds. sec2dhms() { declare -i SS="$1" D=$(( SS / 86400 )) H=$(( SS % 86400 / 3600 )) M=$(( SS % 3600 / 60 )) S=$(( SS % 60 )) [ "$D" -gt 0 ] && echo -n "${D}:" [ "$H" -gt 0 ] && printf "%02g:" "$H" printf "%02g:%02g\n" "$M" "$S" }

Take screenshot through SSH
When connected to a box via ssh you can do a quick screenshot of that box using this command. After that you can rscp it over to your box and look at it.

Find usb device in realtime
Using this command you can track a moment when usb device was attached.

Use a var with more text only if it exists
See "Parameter Expansion" in the bash manpage. They refer to this as "Use Alternate Value", but we're including the var in the at alternative.

Virtual Console lock program
vlock command locks the current console by default. Also you can lock all the consoles on the server by using -a parameter. For details, pl man vlock. ps: Generally speaking , system will not install vlock programme . So you should use ' $ sudo apt-get install vlock ' to install vlock .

SED - Substitute string in next line
source: http://sed.sourceforge.net/sed1line.txt


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