Input and Output Redirection
Input and Output Redirection
This document provides basic descriptions of redirection and pipe commands.
input
By convention, a UNIX command reads input from standard input
(the keyboard). To get a command to read from a file
instead, you need the command, the filename, and the character '<' :
my_command < my_input.
Think of the '<' as an arrow pointing in the direction the
data is flowing, from the file to the command.
output
The output of a UNIX command is sent to standard output (the screen)
by convention. To get a command to send the output into a file instead,
you need the command, the filename, and the character '>' :
my_command > my_output.
The arrow analogy holds true in this direction as well, with the data flowing
from the command to the file.
To append the output of a command to a file without erasing its previous
contents, use the notation : my_command >> my_output.
pipes
If you have a series of commands in which the output of one command
is the input of the next, you can pipe the output through without
saving it in temporary files: first_command | next_command. For
example, if you wanted to print out a sorted version of a file that contained
a list of names and phone numbers, you could use a pipe (as well as
input redirection): sort < my_phone_list | lpr.
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