Most shell commands display information about your workstation screen, standard output. If you redirect the output, you can save the output from a command in a file instead. The output is sent to the file rather than to the screen. At the end of any command, enter:

>filename

For example:

cat file1 file2 file3 >outfile

writes the contents of the three files into another file called outfile. All the information in the original three files is concatenated into a single file, outfile.

When you redirect output with >filename and it is an existing file, the output writes over any information that the file already contains. To append command output at the end of the file, use:

>>filename

instead.

Another example:

(sort -u file1 >output) >&outerr

redirects the result of the sort to the file named output (instead of standard output) and redirects any error messages to the file outerr, which is a record of errors encountered during various sorts.

Suppose you entered:

sort -u filea >output

In this command, you see two redirections:

• Error output from the sort is redirected to standard output, the display screen.
• The result of the sort is redirected to the file named output.

Here is another example of redirection, sending both standard error and standard output to a file. This command produces the program hello and a listing with error messages in a file called hello.list:

c89 -o hello -V hello.c >&hello.list