9.9 Input and Output Redirection

As previously mentioned, many shell commands output information when executed. By default this output goes to a device file named stdout which is essentially the terminal window or console in which the shell is running. Conversely, the shell takes input from a device file named stdin, which by default is the keyboard.

Output from a command can be redirected from stdout to a physical file on the file system using the ‘>’ character. For example, to redirect the output from an ls command to a file named files.txt, the following command would be required:

$ ls *.txt > files.txt

Upon completion, files.txt will contain the list of files in the current directory. Similarly, the contents of a file may be fed into a command in place of stdin. For example, to redirect the contents of a file as input to a command:

$ wc –l < files.txt

The above command will display the number of lines contained in the files.txt file...