OUTPUT REDIRECTION

Any command in Linux will have 3 data streams ,

1. STDIN --> 0
2. STDOUT --> 1
3. STDERR --> 2

These numbers are called DESCRIPTOR.

>--> Redirection to a file.
>> --> Upend to the last line.
2> --> This will get the error.
2>> --> Upend the error.
&> --> Both output & error will be stored in the file.

PIPE SYMBOL or PIPE REDIRECTION

• First command output is the input to the second command.

• cat file1 | less --> Its like Booklet ( so ENTER ENTER --> it will turn like a page , Down arrow and Up arrow )

• cat file1 | more

PATTERN MATCHING or CLOBBING

• * ? [] ! {}
• touch file{a..z}
• touch file{1..100}
• touch file{11,12,17}
• ls -l file[abcd] --> exact match pattern
• ls -l !(file) --> list files which is not having any name with file. Its just exclude.
• To remove all files in one command rm -r file*
• ls -l ??? --> Single character matching
• ls -l ?file --> Character matching
• ls -l file?
• ls -l /var/log/???

VI

• sudo yum install vim
• :set number
• dd --> delete
• copy & past --> yy & c
• cut & past --> dd & c
• 3 & dd --> it will delete 3 lines from the cursor
• shift + g --> Last line
• :1 --> it will go to the first line