Linux, Redirection of Standard Input & Output

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Redirection of Standard Input & Output

In Linux, the standard input device is the keyboard and the standard output device is the display screen. Linux does, however, allow the redirection of both standard input and output to files, for example. In other words, Linux accepts input from files and can direct output to files.

Three symbols are used to indicate redirection to Linux. The symbols are:

Symbol
Meaning

<
Accept input from a file instead of the keyboard

>
Send output to a file instead of the display device

>>
Append output to the end of the indicated file. For example keep a log file.

Redirecting command output to a file

$ ls -alt > dir.lst

$ cat dir.lst

total 68

drwx------ 4 tclark tclark 4096 Feb 24 23:27 .

-rw-rw-r-- 1 tclark tclark 0 Feb 24 23:27 dir.lst

-rw------- 1 tclark tclark 11629 Feb 24 21:24 .bash_history

-rwxrwxr-x 1 tclark tclark 325 Feb 24 21:17 mylogin

-rw------- 1 tclark tclark 4151 Feb 24 21:17 .viminfo

-rwxrwxr-x 1 tclark tclark 208 Feb 19 22:52 test.bsh

drwxrwxr-x 2 tclark authors 4096 Feb 3 23:11 examples

-rw-rw-r-- 1 tclark tclark 0 Feb 3 09:00 example1.fil

-rw-r--r-- 1 tclark authors 0 Jan 27 00:22 umask_example.fil

drwxr-xr-x 8 root root 4096 Jan 25 22:16 ..

-rw-rw-r-- 1 tclark tclark 0 Jan 13 21:13 example2.xxx

-rw-r--r-- 1 tclark tclark 120 Aug 24 2004 .gtkrc

-rw-r--r-- 1 tclark tclark 24 Aug 18 2004 .bash_logout

-rw-r--r-- 1 tclark tclark 191 Aug 18 2004 .bash_profile

-rw-r--r-- 1 tclark tclark 124 Aug 18 2004 .bashrc

-rw-r--r-- 1 tclark tclark 237 May 22 2003 .emacs

-rw-r--r-- 1 tclark tclark 220 Nov 27 2002 .zshrc

drwxr-xr-x 3 tclark tclark 4096 Aug 12 2002 .kde

Appending command output to a file

$ date >> time.txt

$ date >> time.txt

$ date >> time.txt

$

$ cat time.txt

Thu Feb 24 23:31:22 MST 2005

Thu Feb 24 23:31:36 MST 2005

Thu Feb 24 23:31:50 MST 2005

Accepting input from a file

$ less < dir.lst

total 68

drwx------ 4 tclark tclark 4096 Feb 24 23:27 .

-rw-rw-r-- 1 tclark tclark 0 Feb 24 23:27 dir.lst

-rw------- 1 tclark tclark 11629 Feb 24 21:24 .bash_history

-rwxrwxr-x 1 tclark tclark 325 Feb 24 21:17 mylogin

-rw------- 1 tclark tclark 4151 Feb 24 21:17 .viminfo

-rwxrwxr-x 1 tclark tclark 208 Feb 19 22:52 test.bsh

drwxrwxr-x 2 tclark authors 4096 Feb 3 23:11 examples

-rw-rw-r-- 1 tclark tclark 0 Feb 3 09:00 example1.fil

-rw-r--r-- 1 tclark authors 0 Jan 27 00:22 umask_example.fil

drwxr-xr-x 8 root root 4096 Jan 25 22:16 ..

-rw-rw-r-- 1 tclark tclark 0 Jan 13 21:13 example2.xxx

-rw-r--r-- 1 tclark tclark 120 Aug 24 2004 .gtkrc

-rw-r--r-- 1 tclark tclark 24 Aug 18 2004 .bash_logout

-rw-r--r-- 1 tclark tclark 191 Aug 18 2004 .bash_profile

-rw-r--r-- 1 tclark tclark 124 Aug 18 2004 .bashrc

-rw-r--r-- 1 tclark tclark 237 May 22 2003 .emacs

-rw-r--r-- 1 tclark tclark 220 Nov 27 2002 .zshrc

drwxr-xr-x 3 tclark tclark 4096 Aug 12 2002 .kde

(END)

The above book excerpt is from:

Easy Linux Commands
Working Examples of Linux Command Syntax

ISBN: 0-9759135-0-6

Terry Clark

http://www.rampant-books.com/book_2005_1_linux_commands.htm

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