Chapter 3 Pipeline Characters, Redirects, and Environment Variables.

So far, we've learned dozens of commonly used Linux system commands that don't increase productivity if you can't combine them. T his chapter first explains the five modes of redirection technology related to file read and write operations - standard override output redirection, standard appended output redirection, error override output redirection, error appending output redirection, and input redirection, so that the reader can understand the role of each redirect mode through experiments and solve the problem of saving output information. T hen go deep into the pipeline command characters to help the reader master how to use the combination between commands, and further improve the efficiency of the processing of command output values. T hen, by explaining the wildcards and common escape characters on the Linux system command line, you can enter Linux commands with more accurate meaning and help you write Shell scripts for the next chapter. Finally, this chapter analyzes the internal principles of the Bash interpreter in executing Linux commands, and lays a foundation for the reader to grasp the PATH variable and the important environment variables in Linux system.