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Determine MAC address of remote host when you know its IP address
arping sends ARP requests to a neighboring host. This won't work if there is an ARP subnet gateway in the middle. If there is, you'll just get the gateway's MAC address not the host's address you are really trying to get to.

power off system in X minutes
Replace 60 with the number of minutes until you want the machine to shut down. Alternatively give an absolute time in the format hh:mm (shutdown -h 9:30) Or shutdown right away (shutdown -h now)

Clone perms and owner group from one file to another
Copy both perms and owner group from one file to another.

A formatting test for David Winterbottom: improving commandlinefu for submitters
Commandlinefu.com is great but has a few bugs when people are submitting new commands: . 1. There is no preview button. This was a minor inconvenience before, but now is a major problem since new commands won't show up to be edited until they have been moderated. . 2. White space in the description field and in the comments is almost completely lost. People resort to using periods in between paragraphs to force a line break. Indentation of code is ridiculous. . 3. Many characters get munged. . 3a. For example, a less than character in the description gets read as an HTML tag and discarded. In order to type a less than, I've had to type "<" (I hope that comes out right). Unfortunately, when re-editing a command, the HTML entity is turned into a literal less than character, which I have to change back by hand before saving. 3b. Some unicode characters work in the description field, but turn into ugly literal HTML strings when put in the sample output or in an additional command using the $ prefix. . For example, here is a unicode character: ❥ $ Here is the same character after a dollar sign: ❥ . 3c. Some unicode characters don't work anywhere. Bizarrely, it appears to be the most commonly needed ones, such as Latin-1 accented characters. Here are some examples, . Bullet: ?, Center dot: ?, Umlaut u: ?. . 4. Here is an example of the greater than, >, and less than,

Output a SSL certificate start or end date
A quick and simple way of outputting the start and end date of a certificate, you can simply use 'openssl x509 -in xxxxxx.crt -noout -enddate' to output the end date (ex. notAfter=Feb 01 11:30:32 2009 GMT) and with the date command you format the output to an ISO format. For the start date use the switch -startdate and for end date use -enddate.

Find commets in jpg files.
Finds comments in jpg files, but I can't figure out how to exclude (in output) files without comments.

Print only the odd lines of a file (GNU sed)
The tilde address operator is an extension of GNU sed. It won't work with POSIX sed.

ascii digital clock
# ### ### # # ### ### # # # ## # # ### # # # # ### ## # # # # # # ### # # # # ### # # # # # ### ##### # # ##### # # # ### # # ### # # # # # ### # # ### # # ##### ### ### # ##### ### ##### #

Get a range on line with sed (first two)
Get the two first lines of a file and quit.

drop first column of output by piping to this
An advantage is that this doesn't modify remained string at all. One can change {0,1} with {0,n} to drop several columns


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