15.D: Appending Files with <<

15: File Utilities

15.B: The cat command

The symbol < stands for redirect standard input. It is used to allow you to take input from a file instead of input from the keyboard. One use of this symbol would be a datafile for input to a Fortran program.

The similar symbol > stands for redirect standard output. It is used to allow you to take input from a file instead of input from the keyboard. One One use of this command would be to combine it with the cat command to create a file. To create a file use cat > followed by the filename and press return. Unix will give you a new line and wait for you to type the text for the file. When you are done typing text hold down the "control" key (sometimes labeled "Ctrl") and the "d" key at the same time to end the file (^d).

Try creating a file named "hello" with the text:

Hello World!
I am here!

Now type a ^d (control d) to end your file.

Another way to use cat and < to create a file is to take the input from a series of other files. Just put the names of the input files before the <. For instance:
> cat hello .forward > old.text

Use the cat command to view the new file. (Quiz)
Review the cat command

If you use this method, be sure to not use the same name for input and output files. Cat creates the file first and will therefore erase your input file before writing the output file. In the next section we will use the append symbol to input from and output to the same file.

15.D: Appending Files with <<

15: File Utilities

15.B: The cat command