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Redirecting Input and Output

File Redirection

The output from most commands is sent to standard output, usually the screen. You can, however, redirect output from a command into a file instead of to your screen.

To redirect output to a file, you would type:

Some examples:

In the above examples, if the specified file already existed, it would be overwritten. If you want to append output to a currently existing file instead of overwritting it, you would type:

For example:

The input to most commands comes from standard input, usually the keyboard. You can however, redirect input to a command to come from a file rather than the keyboard.

To redirect input to a command, you would type:

Some examples:

You can also redirect standard output to a file while redirecting standard error to the screen by typing:

For example, if you were running a C or fortran program and you wanted the results to go to a file, but the error messages to go to the screen, you could type:

Output Redirection

The previous section describes redirecting output to file or input from a file. You can also redirect the output of one command into the input of another command by using the | symbol-- the "pipe" symbol. You would type:

Some examples:

You can also redirect the output of a command to a file and to the screen or another command using the tee command. You would type:

The first example will send a copy of the output to a file and a copy of the output to the screen. The second example will send a copy of the output to a file and send a copy of the output on to the next command.

Some examples:

Last updated:
February 03, 2011

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