POSIX basics

POSIX -Portable operating system Interface. stdin, stdout, and stderr are three Input/Output standard streams. These values are following

0: stdin

1: stdout

2: stderr

1. stdin is the standard input stream. This accepts text as its input.
2. stdout is the standard output stream to write the output data.
3. stderr is the standard output stream to show error messages.

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Pipe

consider the following command.

ls | cat

in this command, the ls output (stdout) is piped into another command(cat).

Redirect

The > redirection symbol works with stdout by default.

1> To stdout redirect. > is shorthand for 1>

2> To stderr redirect

Examples:

Command 1> capture.txt

The above command will save the stdout into the capture.txt file.

Command 2> capture.txt

The above command will save the stderr into the capture.txt file.

Command 1> capture.txt 2> error.txt

The above command will save the stdout in capture.txt and stderr in error.txt file

Command 1> capture.txt 2>&1

The above command will save the stdout and stderr into capture.txt file