stderr are all important standard input/output streams that are used to manage input and output from command line programs. So, here’s a quick overview for each of them.
stdin: This stands for standard input, and it is the input stream that carries data into a program. This data can come from a variety of sources, including keyboard input or input piped from another program.
stdout: This stands for standard output, and it is the output stream that a program uses to send data back to the user. This data is typically printed to the command line, and it can include text or other types of data, such as images.
stderr: This stands for standard error, and it is the output stream that a program uses to send error messages to the user. This stream is typically used to report errors that occur during program execution, such as syntax errors or file not found errors.
stderr are all associated with the CLI. However, it is possible to redirect these streams to different sources using various Linux commands, such as
2>. For example, the
> operator can be used to redirect the output of a program to a file instead of printing it to the command line.
The most typical and popular idiom in this context is
2>&1. It is used to redirect the stderr stream to the same location as the stdout stream.
By default, stdout and stderr are separate output streams. If you run a command, and it produces output, that output will be sent to stdout. If there is an error during the command’s execution, the error message will be sent to stderr.
Sometimes, you may want to capture both stdout and stderr and save them to the same location. In that case, you can use the
2>&1 idiom to redirect stderr to the same location as stdout.
Here’s an example of how to use the
tail -n50 error.log > output.txt 2>&1
In this example, the
> operator is used to redirect stdout to the file output.txt. The
2>&1 idiom is used to redirect stderr to the same location as stdout. This means that both the output and any error messages will be saved to the file output.txt.
Note(s): The order of the redirection matters here. The
2>&1 part of the command must come after the
> part. If you reverse the order, stderr will still be sent to the command line, not the file.
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