Good for automating reports that need to run from between two dates.

the -A argument forwards your ssh private keys to the host you're going to. Useful in some scenarios where you have to hop to one server, and then login to another using a private key.

queries local memcached for stats, calculates hit/get ratio and prints it out.

Ran as the postgres user, dumps each database individually. It dumps with the create statements as well, so you can just 'zcat $x-nightly.dmp.gz | psql' to reimport/recreate a database from a backup.

Find files that are older than x days in the working directory and list them. This will recurse all the sub-directories inside the working directory.

By changing the value for -mtime, you can adjust the time and by replacing the ls command with, say, rm, you can remove those files if you wish to.

Note that the file at the given path will have the contents of the (still) deleted file, but it is a new file with a new node number; in other words, this restores the data, but it does not actually "undelete" the old file.

I posted a function declaration encapsulating this functionality to http://www.reddit.com/r/programming/comments/7yx6f/how_to_undelete_any_open_deleted_file_in_linux/c07sqwe (please excuse the crap formatting).

This runs a command continuously, restarting it if it exits. Sort of a poor man's daemontools. Useful for running servers from the command line instead of inittab.

An easy way to create aliases for moving between many directories

Long before tabbed terminals existed, people have been using Gnu screen to open many shells in a single text terminal. Combined with ssh, it gives you the ability to have many open shells with a single remote connection using the above options. If you detach with "Ctrl-a d" or if the ssh session is accidentally terminated, all processes running in your remote shells remain undisturbed, ready for you to reconnect. Other useful screen commands are "Ctrl-a c" (open new shell) and "Ctrl-a a" (alternate between shells). Read this quick reference for more screen commands: http://aperiodic.net/screen/quick_reference

I often need to add a timestamp to a file, but I never seem to remember the exact format string that has to be passed to the date command to get a compact datetime string like 20090220T231410 (i.e yyyymmddThhmmss, the ISO 8601 format popular outside the US)

mplayer -vo caca will give you a similar result but in color

instead of writing:

if [[ "$1" == "$2" ]]; then

echo "$1 is equal $2"

else

echo "$1 differs from $2"

fi

do write:

[[ "$1" == "$2" ]] && echo "$1 is equal $2" || echo "$1 differs from $2"

This finds a process id by name, but without the extra grep that you usually see. Remember, awk can grep too!

search file for string1 or string2