IO Redirection

Introduction#

Generally a command takes inputs from terminal and outputs back to terminal. Normally a command reads input from keyboard and outputs result to the screen. Here is the importance of Input/Output Redirection

Syntax#

• [fd]<file
• [fd]<&fd
• [fd]<&-
• [fd]>file
• [fd]>&fd
• [fd]>&-
• [fd]>|file
• [fd]>>file
• [fd]<>file
• [fd]<<[-] word
  …
  word

Remarks#

Resources

• The POSIX ‘Shell Command Language’ section on ‘Redirection’

Output Redirection

Usually output of a command goes to the terminal. Using the concept of Output redirection, the output of a command can be redirected to a file. So insted of displaying the output to the terminal it can be send to a file. ’>’ character is used for output redirection.

$ pwd > file1
$ cat file1
/home/cg/root

In the above example, the command the output ‘pwd’ of the command is redirected to a file called ‘file1’.

Input Redirection

The commands normally take their input from the standard input device keyboard. Using Input redirection concept, we can have their input redirected from a file. To redirect standard input from a file instead of the keyboard, the ’<’ character is used.

$ cat file1 
monday
tuesday
wednsday
thursday
friday
saturday
sunday

The above is the content of file1

$ sort < file1
friday
monday
saturday
sunday
thursday
tuesday
wednsday

here insted of taking input from keyboard, we redirected it from the file1 and sort it in ascending order.