Redirecting Input /Output

The standard Output of command , which normally display on the terminal can be redirected into a file. Similarly standard error, which normally display on the terminal can be redirected into a file.

Common redirection operator

> : command>file : output command to file

>> : command>>file : Append output of command to file

< : command>file : receive input from file

2> : command2>file : error from command to file

2>> : command2>>file : append

Example:

#find /etc –name passwd

this command will search for all file name passwd in /etc and its subdirectories

now we can redirtect the standard outpout

#find /etc –name passwd > output

output is a file where command output will be stored. Standard error is still displayed on the screen

#cat output

If the target file of the file redirection with > already exists, the existing file will be overwritten. To append data to an existing file use >> to redirect instead of >

#find /etc –name passwd >> output

Redirecting standard Error

We can redirect standard error with 2>

#find /etc –name passwd 2>errorfile

standard output is displayed on the screen , redirect further standard error, appending to the same file with 2>>

#find /etc/ -name passwd 2>>errorfile

#cat errorfile

Symbolic links:

A symbolic link point to another file. We can display the link name and the referenced file by ‘ls –l’

#ls –l pf

lrwxrwxrwx 1 root root pf->/etc/passwd

file type: l for symbolic link

the content of the symbolic link is the name of the file that is referenced

Syntax:

Ln –s filename [linkname]

Example:

Ln –s /etc/passwd password

There are seven fundamental file type

- : regular file

d : symbolic link

b : block special file

c : character special file

p : named file

s : socket

character special file are used to communicate with hardware one character at a time. Block special file is used to communicate with hardware a block of data at a time : 512 bytes, 1024 bytes, 2048 bytes

ls –l /dev |less { to check c and b files}

named pipe type of file that passes data between processes. It stores no data itself socket file are used for inter process communication.