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Count the frequency of every word for a given file
Counts the frequency of words in a file

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Filter the output of a file continously using tail and grep
The OPs solution will work, however on some systems (bsd), grep will not filter the data, unless the --line-buffered option is enabled.

Create a CD/DVD ISO image from disk.
Many like to use 'dd' for creating CD/DVD iso images. This is bad. Very bad. The reason this is, is 'dd' doesn't have any built-in error checking. So, you don't know if you got all the bits or not. As such, it is not the right tool for the job. Instead, 'reaom' (read optical media) from the wodim package is what you should be using. It has built-in error checking. Similarly, if you want to burn your newly creating ISO, stay away from 'dd', and use: $ wodim -v -eject /path/to/image.iso

Copy files from multiple directories into one directory

Delicious search with human readable output
You can install filterous with $ sudo apt-get install libxslt1-dev; sudo easy_install -U filterous

Connect-back shell using Bash built-ins

Extract raw URLs from a file
you can also use cut instead of awk. less powerful but probably faster. ;)

Listing today’s files only

Find out how old a web page is
I used to use the Firefox "View page info" feature a lot to determine how stale the web page I was looking at was. Now that I use mostly Chrome I miss that feature, so here is a command line alternative using wget. The -S says to display the server response, the --spider says to not download any files/pages, just fetch the header. The output goes to stderr, so to grep it you use 2>&1 to combine the stderr stream with stdout, the pipe that to grep for Last-Modified. You can use curl instead if you have it installed, like this: $ curl --head -s http://osswin.sourceforge.net | grep Mod


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