Redirecting Input /Output,Symbolic links,Checking Free Space In Linux

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.

Checking Free Space:

In order to check the free and usage space per file system and directory and each sub directory we have two command

1. df
2. du

the ‘df’ command reports on a per file system basis. It report total disk space , disk space used , disk space free

#df –h

-h         : used multipliers such as G or M for gigabytes and Megabytes

The ‘du’ command reports the number of kilobytes contained by the items within a directory

#du –s

#du –h

-s         :           used to request only the summary directory information

#du –s /etc

Thanks,