Documentation / 18.3. Redirecting Command Events
	18.2. Writing Shell Scripts		18.4. Using Aliases

Redirecting Command Events

Each command can use three channels, either for input or output:

Standard Output. This is the default output channel. Whenever a command prints something, it uses the standard output channel.
Standard Input. If a command needs input from users or other commands, it uses this channel.
Standard Error. Commands use this channel for error reporting.

To redirect these channels, there are the following possibilities:

Command > File

Saves the output of the command into a file, an existing file will be deleted. For example, the ls command writes its output into the file listing.txt:

ls > listing.txt

Command >> File

Appends the output of the command to a file. For example, the ls command appends its output to the file listing.txt:

ls >> listing.txt

Command < File

Reads the file as input for the given command. For example, the read command reads in the content of the file into a variable:

read a < foo

Command1 | Command2

Redirects the output of the left command as input for the right command.

Every channel has a file descriptor: 0 (zero) for standard input, 1 for standard output and 2 for standard error. It is allowed to insert this file descriptor before a < or > character. For example, the following line searches for a file starting with foo, but suppresses its errors by redirecting it to /dev/null:

find / -name "foo*" 2>/dev/null