commands

Expansions

Brace expansion

touch {apple, banana, orange}
touch file_{1..100}
with zero padding: touch file_{01..100}

echo {1..10..2}
get numbers between 1 and 10, counting by 2.

echo {A..z}

echo {w..d..2}


Number of output
ls -1 | wc -l

View top and bottom of file:
head
tail

cp -v * ../otherfolder 1>../success.txt 2>../error.txt
1 and 2 represent standard output and standard error respectively.
> indicates redirecting them somewhere else.

Also:
cp -v * ../otherfolder &>../log.txt (Same thing as earlier)

bitbucket:
ls > /dev/null

Using awk to just get a column (12)
grep -i break-in auth.log | awk {'print $12'}

Set ping count
ping -c 1

Get response time only from ping result
ping -c 1 example.com | grep 'bytes from' | cut -d = -f 4

BASH Script

declare -i a=123  (integer)
declare -r b=123 (read only) 
declare -l c="ABCD" (convert to lower case)
declare -u d="abcd" (convert to upper case)

tldp.org/LDP/abs/html/internalvariables.html