Quick Start Guide

takes you to the beginning, and [End] to the end of the document. To end the

viewing mode, press [Q].

Instead of less, you can also use the older program more. It has basically the

same function—however, it is less convenient because it does not allow you to

scroll backwards. Use [Space] to move forward. When you reach the end of the

document, the viewer closes automatically.

cat

The cat command displays the contents of a le, printing the entire contents to

the screen without interruption. As cat does not allow you to scroll it is not very

useful as viewer but it is rather often used in combination with other commands.

7.10 Redirection and Pipes

Sometimes it would be useful if you could write the output of a command to a le

for further editing or if you could combine several commands, using the output of

one command as the input for the next one. The shell oers this function by means

of redirection or pipes.

Normally, the standard output in the shell is your screen (or an open shell window)

and the standard input is the keyboard. With the help of certain symbols you can

redirect the input or the output to another object, such as a le or another command.

Redirection

With > you can forward the output of a command to a le (output redirection),

with < you can use a le as input for a command (input redirection).

Pipe

By means of a pipe symbol | you can also redirect the output: with a pipe, you

can combine several commands, using the output of one command as input for

the next command. In contrast to the other redirection symbols > and <, the use

of the pipe is not constrained to les.

7.10.1 Examples for Redirection and Pipe

To write the output of a command like ls to a le, enter

ls -l > filelist.txt

This creates a le named filelist.txt that contains the list of contents of

your current directory as generated by the ls command.

However, if a le named filelist.txt already exists, this command overwrites

the existing le. To prevent this, use >> instead of >. Entering

ls -l >> filelist.txt

Shell Basics 103