Written for linux, the real example is how to produce ascii text graphs based on a numeric value (anything where uniq -c is useful is a good candidate).

Replace FILE with a filename (or - for stdin).

Use the find command to match certain files and summarise their total size in KBytes.

A variation of a script I found on this site and then slimmed down to just use awk. It displays all users who have attempted to login to the box and failed using SSH. Pipe it to the sort command to see which usernames have the most failed logins.

When you fill a formular with Firefox, you see things you entered in previous formulars with same field names. This command list everything Firefox has registered. Using a "delete from", you can remove anoying Google queries, for example ;-)

Extracted from http://www.howtogeek.com/wiki/Recursively_Add_Changed_Files_to_Subversion

Lists the local files that are not present in the remote repository (lines beginning with ?)

and add them.

It will return a ranked list of your most commonly-entered commands using your command history

List files above a given size threshold.

This command will display only the hosts that are active in the network.

Are there any creative pieces of music that can be created using beep and the shell? I'd love to hear it!

This command will sort the contents of FILENAME by redirecting the output to individual .txt files in which 3rd column will be used for sorting. If FILENAME contents are as follows:

foo foo A foo

bar bar B bar

lorem ipsum A lorem

Then two files called A.txt and B.txt will be created and their contents will be:

A.txt

foo foo A foo

lorem ipsum A lorem

and B.txt will be

bar bar B bar

I find it ugly & sexy at the same time isn't it ?

Searches /var/log/secure for smtp connections then lists these by number of connections made and hosts.

Searches the /var/log/secure log file for Failed and/or invalid user log in attempts.

Here is a command line to run on your server if you think your server is under attack. It prints our a list of open connections to your server and sorts them by amount.

BSD Version:

I find this terribly useful for grepping through a file, looking for just a block of text. There's "grep -A # pattern file.txt" to see a specific number of lines following your pattern, but what if you want to see the whole block? Say, the output of "dmidecode" (as root):

Will show me everything following the battery block up to the next block of text. Again, I find this extremely useful when I want to see whole blocks of text based on a pattern, and I don't care to see the rest of the data in output. This could be used against the '/etc/securetty/user' file on Unix to find the block of a specific user. It could be used against VirtualHosts or Directories on Apache to find specific definitions. The scenarios go on for any text formatted in a block fashion. Very handy.

Some commands (such as netcat) have a port option but how can you know which ports are unused?