Wildcards, Alias, Grep, pipes, Shell variables, Environment variables Linux Administration

Linux Administration 
wildcard * ? []
Examples 
delete music files .mp3  >10 

rm musicfiles-1?.mp3

?- only one character 
rm music file-?.mp3

* one or more 
rm music-file-*

ls

rm txtfile-[1234]

rm file-moves-[Aa]

PIPES
pipes || are used to direct the output from one command to another

GREP
finding the matching patern

cat fruits | grep Orange
onlu 

cat vegetables |grep carrot

 cat vegetables |grep carrot | sort

uniq : unique no and count

cat Numbers | uniq -c

cat fruits | grep ap | sort

Alias in shell
shortcut to your own command
To list already seted alias ->  alias

uptime
alias u='uptime'
u
alias doc = 'libreoffice -writer'
doc

Linux environment variables:
=> Storing a value in a location filename, text,a num, other type of data;
=> Application setting to different application
Private to currently running shell
'MYVAR = private; OURVAR = shared; printenv'
shell executes the printenv  it exports as OURVAR but not as MYVAR
print env  passed to child variables

To see shell variables :
set | less
HISTFILE
To print environment variables 
printenv
user =cam 
 

MYTESTVAR='This my ada'
Set | grep MYTESTVAR 
>'This my ada'
exist only shell session 
printenv | grep MYTESTVAR
>no data

echo $MYTESTVAR"
shell to environment var
export $MYTESTVAR"
printenv | grep MYTESTVAR
echo $MYTESTVAR"

Demoting the env var
export -n MYTESTVAR
printenv | grep MYTESTVAR
>no data

MYDIR='/home/Musicc'
echo $MYDIR

ls $MYDIR 
setting the shell variables
vi ~/.bash_profile
setting the env variables
vi /etc/profile