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eavesdrop
Record off the microphone on a remote computer and listen to it live through your speakers locally.

Watch memcache traffic
View all memcache traffic

Export OPML from Google Reader

View non-printing characters with cat
Useful to detect number of tabs in an empty line, DOS newline (carriage return + newline). A tool that can help you understand why your parsing is not working.

Recursive search and replace (with bash only)
Replaces a string matching a pattern in one or several files found recursively in a particular folder.

Shows users and 'virtual users' on your a unix-type system
Shows a list of users that currently running processes are executing as. YMMV regarding ps and it's many variants. For example, you might need: $ ps -axgu | cut -f1 -d' ' | sort -u

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"

Resample a WAV file with sox
Change the sample rate with sox, the swiss army knife of sound processing.

list block devices
Shows all block devices in a tree with descruptions of what they are.

prevent large files from being cached in memory (backups!)
We all know... $ nice -n19 for low CPU priority.   $ ionice -c3 for low I/O priority.   nocache can be useful in related scenarios, when we operate on very large files just a single time, e.g. a backup job. It advises the kernel that no caching is required for the involved files, so our current file cache is not erased, potentially decreasing performance on other, more typical file I/O, e.g. on a desktop.   http://askubuntu.com/questions/122857 https://github.com/Feh/nocache http://packages.debian.org/search?keywords=nocache http://packages.ubuntu.com/search?keywords=nocache   To undo caching of a single file in hindsight, you can do $ cachedel   To check the cache status of a file, do $ cachestats


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