This appends (-A) a new rule to the INPUT chain, which specifies to drop all packets from a source (-s) IP address.

Self-referential use of wget.

great for outputting tweets from cron jobs and batch scripts

Changes standard mysql client output to 'less'.

In another words makes query results of mysql command line client to look much better.

it compresses the files and folders to stdout, secure copies it to the server's stdin and runs tar there to extract the input and output to whatever destination using -C. if you emit "-C /destination", it will extract it to the home folder of the user, much like `scp file user@server:`.

the "v" in the tar command can be removed for no verbosity.

checks which files are not under version control, fetches the names and runs them through "svn add". WARNING: doesn't work with white spaces.

The tee (as in "T" junction) command is very useful for redirecting output to two places.

the addition of ".bk" to the regular "pie" idiom makes perl create a backup of every file with the extension ".bk", in case it b0rks something and you want it back

The "g" at the end is for global, meaning replace all occurrences and not just the first one.

If you bork your terminal by sending binary data to STDOUT or similar, you can get your terminal back using this command rather than killing and restarting the session. Note that you often won't be able to see the characters as you type them.

Useful when quickly looking for a commit id from a branch to use with git cherry-pick.

This spiders the given site without downloading the HTML content. The resulting directory structure is then parsed to output a list of the URLs to url-list.txt. Note that this can take a long time to run and you make want to throttle the spidering so as to play nicely.

This recursively downloads all images from a given website to your /tmp directory. The -nH and -nd switches disable downloading of the directory structure.

This runs the uptime command every 30 seconds to avoid an SSH connection dropping due to inactivity. Granted there are better ways of solving this problem but this is sometimes the right tool for the job.

The --force option bypasses the warning if files are already in SVN.

This counts the number of httpd processes running.

Simple use of find and grep to recursively search a directory for files that contain a certain term.

You will be prompted for a password unless you have your public keys set-up.

Really useful for when you have a typo in a previous command. Also, arguments default to empty so if you accidentally run:

you can correct it with

Uses shell expansion to create a back-up called file.txt.bak

This grabs all lines that make an instantation or static call, then filters out the cruft and displays a summary of each class called and the frequency.

Sed stops parsing at the match and so is much more effecient than piping head into tail or similar. Grab a line range using

Using xargs is better than:

as the -exec switch uses a separate process for each remove. xargs splits the streamed files into more managable subsets so less processes are required.