Newbie School: about output redirection in LinuxShell

Article Title: newbie School: about output redirection under LinuxShell. Linux is a technology channel of the IT lab in China. Including desktop applications, Linux system management, kernel research, embedded systems, open source, and other basic categories. Linux Shell environments support input and output redirection, expressed by symbols "<" and ">. 0, 1, and 2 indicate the standard input, standard output, and standard error information output, which can be used to specify the standard input or output to be redirected. For example, 2> a.txt outputs the error information to file a.txt.

At the same time, you can also implement redirection between the three standard input and output. For example, you can use 2> & 1 to redirect the error message to the standard output.

In Linux, there is also a special file/dev/null, which is like a bottomless pit, and all the information redirected to it will disappear without a trace. This is very useful. When we do not need to display all information about the program, we can redirect the output to/dev/null.

To disable normal output and error information, redirect both standard output and standard errors to/dev/null. For example:

# Ls 1>/dev/null 2>/dev/null

Another way is to redirect errors to standard output and then to/dev/null, for example:

# Ls>/dev/null 2> & 1

Note: The order here cannot be changed. Otherwise, the desired effect cannot be reached. In this case, the standard output is redirected to/dev/null and the standard error is redirected to the standard output, since the standard output has been redirected to/dev/null, the standard error will also be redirected to/dev/null, so everything will be quietly :-)

+:

Make> & make_log

This means to redirect both standard output and error output. make> out only redirects standard output !!!!!

> Log indicates to redirect the standard output to the file log.
> & Log indicates that both the standard output and error output are directed to the file log, which is equivalent to> log 2> & 1