Check These Out
Requires netcat.
A null operation with the name 'comment', allowing comments to be written to HISTFILE. Prepending '#' to a command will *not* write the command to the history file, although it will be available for the current session, thus '#' is not useful for keeping track of comments past the current session.
watch is a command especially designed for doing this job
Instead of opening your browser, googling "whatismyip"...
Also useful for scripts.
dig can be found in the dnsutils package.
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"
This causes cp to detect and omit large blocks of nulls. Sparse files are useful for implying a lot of disk space without actually having to write it all out.
http://en.wikipedia.org/wiki/Sparse_file
You can use it in a pipe too:
$ dd if=/dev/zero bs=1M count=5 |cp --sparse=always /dev/stdin SPARSE_FILE
http://public-dns.info gives a list of online dns servers. you need to change the country in url (br in this url) with your country code. this command need some time to ping all IP in list.
Shorter version, works with multiple words.
The (in)famous "FizzBuzz" programming challenge, answered in a single line of Bash code. The "|column" part at the end merely formats the output a bit, so if "column" is not installed on your machine you can simply omit that part. Without "|column", the solution only uses 75 characters.
The version below is expanded to multiple lines, with comments added.
for i in {1..100} # Use i to loop from "1" to "100", inclusive.
do ((i % 3)) && # If i is not divisible by 3...
x= || # ...blank out x (yes, "x= " does that). Otherwise,...
x=Fizz # ...set x to the string "Fizz".
((i % 5)) || # If i is not divisible by 5, skip (there's no "&&")...
x+=Buzz # ...Otherwise, append (not set) the string "Buzz" to x.
echo ${x:-$i} # Print x unless it is blanked out. Otherwise, print i.
done | column # Wrap output into columns (not part of the test).