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Optimal way of deleting huge numbers of files
This command works by rsyncing the target directory (containing the files you want to delete) with an empty directory. The '--delete' switch instructs rsync to remove files that are not present in the source directory. Since there are no files there, all the files will be deleted. I'm not clear on why it's faster than 'find -delete', but it is. Benchmarks here: https://web.archive.org/web/20130929001850/http://linuxnote.net/jianingy/en/linux/a-fast-way-to-remove-huge-number-of-files.html

cat a bunch of small files with file indication
If you have a bunch of small files that you want to cat to read, you can cat each alone (boring); do a cat *, and you won't see what line is for what file, or do a grep . *. "." will match any string and grep in multifile mode will place a $filename: before each matched line. It works recursively too!!

Query ip pools based on successive netnames via whois
Useful if you f.i. want to block/allow all connections from a certain provider which uses successive netnames for his ip blocks. In this example I used the german Deutsche Telekom which has DTAG-DIAL followed by a number as netname for the dial in pools. There are - as always ;) - different ways to do this. If you have seq available you can use $ net=DTAG-DIAL ; for i in `seq 1 30`; do whois -h whois.ripe.net $net$i | grep '^inetnum:' | sed "s;^.*:;$net$i;" ; done or without seq you can use bash brace expansion $ net=DTAG-DIAL ; for i in {1..30}; do whois -h whois.ripe.net $net$i | grep '^inetnum:' | sed "s;^.*:;$net$i;" ; done or if you like while better than for use something like $ net=DTAG-DIAL ; i=1 ; while true ; do whois -h whois.ripe.net $net$i | grep '^inetnum:' | sed "s;^.*:;$net$i;" ; test $i = 30 && break ; i=$(expr $i + 1) ; done and so on.

Using tput to save, clear and restore the terminal contents
Very useful for interactive scripts where you would like to return the terminal contents to its original state before the script was run. This would be similar to how vi exits and returns you to your original terminal screen. Save and clear the terminal contents with: $tput smcup Execute some commands, then restore the saved terminal contents with: $tput rmcup

Create md5sum of a directory

watch your network load on specific network interface
-n means refresh frequency you could change eth0 to any interface you want, like wlan0

disable history for current shell session
this will cause any commands that you have executed in the current shell session to not be written in your bash_history file upon logout

Use color grep by default
Alias the grep command to show colored results by default.

Transfers clipboard content from one OS X machine to another
This uses ssh to transfer the contents of one Mac's clipboard to another's. This only works with plain text, sadly. Trying to transfer images will just clear out the remote machine's clipboard, and rich text will be converted to plain text. Using the "Remote Login" must be enabled on the remote machine (via System Preferences' Sharing panel) for this to work.

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"

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