Linux basics: pipelines and redirection

Basics of Linux: Pipeline and redirection do not reinvent the wheel. One of the core concepts of open-source culture is not to reinvent the wheel. Many open-source software is a combination of existing software, code, and functions, just like assembling machines through parts, opening and sharing of source code makes this possible, and greatly improves efficiency and productivity. In Linux, most of the commands for pipelines and redirection are simple, and few complex functions are available. Each Command usually only implements one or more simple functions, we can combine commands of different functions to achieve a complex function. In Linux, almost all commands return data in plain text (and because the commands run in CLI), while plain text data is the input format of most commands, this makes multi-command collaboration possible. In Linux, we provide pipelines and redirection mechanisms for command behavior. Multi-command collaboration is achieved through pipelines and redirection. Command Line shell data streams are defined as follows: Name Description No. Default stdin standard input 0 keyboard stdout standard output 1 terminal stderr standard error 2 terminal commands receive parameters or data through stdin, an error is output through stdout or stderr. Through pipelines and redirection, we can control CLI data stream redirection: keyword definition example> redirect stdout to file (overwrite) echo "hello world"> outfile ls-l> outfile> redirects stdout to a file (append) echo "hello world"> outfile date> outfile 2> redirect stderr to a file (overwrite) ls-l nofile 2> outfile 2> & 1 combine stderr with stdout ls nofile> outfile 2> & 1 <redirect stdin grep keyword </etc/passwd, find the line output pipeline with the keyword in the passwd file: | use the stdout of one command as the stdinls-l of another command | grep keyword find/-user shuangde 2>/dev/null | grep Video/dev/null all output is put here automatically discard, like a waste bin, pipelines are usually used to combine different commands to implement a complex function redirection. They are usually used to save the output or error information of a command, it can be used to record execution results or save error messages to a specified file.