Descritpiton of Commands Widely Used in Pattern Matching /Regular Expressions/PERL Scripting

**************Pattern  Matching********************

*  =>  Including allCharacters including "Nothing". Matches any no of Characters.
?  =>  Including all Characters exactly one Match not includes  "Nothing".

a*b  =>  Matches all files which will Start with Letter  a  and End with b.
*a    => Matches  all Files which will end with letter a.
a*  => Matches  all Files  which will start with the Letter  a.
a?b  => Matches  all the file  which will start with a  and end with b including one more character in Middle.
?ab  => Matches  Files  which will start with any single Letter and ends with  "ab".
ab?  => Matches  files which will start with ab and ends with any more character.
[abc]  =>  Exactly Matches one of "a or b or c".
[!abc] or [^abc] => Exactly Matches one Character  not including "a,b or c".
[c-y] => Matches any character  between c  and  y.

Learning UNIX/LINUX Commands for Basic Operations.

Learning    UNIX/LINUX   Commands  for  Basic  Operations.

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Index of Commands
cat - display or concatenate files
cd - change directory
chmod - change the permissions on a file or directory
cp - copy a file
date - display the current date and time
diff - display differences between text files
file - determine the type of a file
find - find files of a specified name or type
ftp - file transfer program
grep - searches files for a specified string or expression
gzip - compress a file
help - display information about bash builtin commands
info - read online documentation
kill - kill a process
lpr - print out a file
ls - list names of files in a directory
man - display an on-line manual page
    mkdir - make a directory
more - scan through a text file page by page
mv - move or rename files or directories
nice - change the priority at which a job is being run
passwd - change your password
ps - list processes
pwd - display the name of your current directory
quota - disk quota and usage
rm - remove files or directories
rmdir - remove a directory
sort - sort and collate lines
ssh - secure remote access
tar - create and use archives of files

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whoami          => to Know the USER name
pwd         => Gives Details About Present Working Directory

*************List the Details****************
ls         => List out The Files.
ls   -a         => List Out all files Including Hidden Files.
ls    -l         => List  all files with Permissions.

***********CHANGE DIRECTORY*****************
cd  [Directory_Name]        => Change Directory
cd                  => Changes to HOME Directory
cd  -                => Changes to Previous Directory
cd  ../                => Move 1 Directory Back
cd  ./                => Represents the Present Directory

**********COPY***************
cp  [file1] [file2]            => Copies the File1 to File2
cp  [file1] [file2]  [Path_Directory]    =>When there are morethan one file it should be the path of Directory.

***********Create Directory***************
mkdir          => Make or Create Directory
mkdir  -p  del1/del2/del3  => Creates the Multiple Directories with Parent as del1 and next and so on.


***********Remove Files  and Folders****************
rm -v  [file_name]    => removes the File.{-v => Represents Verbose}
rm  -r  [directory]    => Removes the Directory  even it is Recursive.{-r  =Represent Recursive}
rm  -f  [directory or file]  => Removes either DIrectory  or FIle{ -f  => Represents  Force.}
rmdir  -v  [Empty_Directory_name] => Removes Only Empty Directories.{-v => Represents Verbose}

*****************Move***********************
mv  [file1]  [file2]        => the Contents of File1 is moved into File2.it is Nothing but Renaming.
mv  [file1]  [Directory_Path]     => Moves the file from Original Place to Mentioned Path.
mv  [file1]  [file2]  [Directory_Path]  => Moves all of the mention Files into  Given Directory.

***********Change MODE ****************************
chmod  777  [file_name]  => Update  Previous Values with the New Values.
permissions for  Admin,user,group
permissions  are  -read,write and execute-

*********Password**********************
passwd  [ENTER_OLD_PASSWORD]  [ENTER NEW PASSWORD]

*******************ShortCUT Keys for Working Under  UNIX *********************

Control-a         => Move to beginning of line
Control-e         =>Move to end of line
Alt-f               =>Move forward one word
Alt-b               =>Move backwards one word
Control-l         =>Clear screen, leaving current lineg
Tab                 =>Try to automatically complete path
ctrl + c           => to end the Process while entering the input through Keyboard.





**********Important  Things to Remember**************************
Control-c            Cancel (kill) foreground job
Control-z             Pause foreground job
jobs                     List current jobs (started in this command-line)
kill %n                 Kill job number n
killall                 name Kill all processes called name
ps                      Show all running processes (distinct from jobs) regardless of how they were started
fg %n                 Bring job number n to foreground
bg %n                 Run job number n in background
program &             Start program in background
nohup program             Run program in background so it will not stop if you log out. stdout and stderr  are redirected to the file nohup.out. Advanced users might like to look at screen instead.


**************PIPES**************************
Definition :::--  a pipe can be used to connect stdout of one command to the stdin of another