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Shell is a program written in C language, which is a bridge for users to use Linux. Shell is both a command language and a programming language.

This article introduces you to some practical and interesting knowledge of Shell, which is not well known, and can be used as a dessert after tasting shell staple food.

First, popularize a few facts that you may not know:

Shell was born almost at the same time as the Unix operating system, and the first Unix Shell was rewritten by Ken Thompson in 1971, based on the model Shell on Multics, and named Thompson sh. Even the later popular bash (a variant of shell) is actually older than all the current popular Linux kernel, and it can be said that on the Linux system, there was Shell before Kernel.

The default Shell in most of the current * nix and MacOS operating systems is bash,bash created by Brian Fox in 1987, the full name Bourne Again shell (bash).

You may have heard that besides bash, there are Bourne shell (sh), Korn shell (ksh), C shell (including csh and tcsh), but did you know that there are about 50 different shell on this planet? To learn more about them, please refer to http://www.freebsd.org/ports/shells.html.

Every month, a ranking of programming languages is given on tiobe to show the popularity of various languages. The ranking index combines the number of engineers using the language worldwide, the number of courses taught, and the number of third-party vendors. As of November 2019, tiobe ranked 22nd in the programming language rankings with an index of 0.56%. If you include its awk 0.21% and tcl 0.146%, it will probably rank 14th. Note that bash's homologous siblings such as csh and ksh are not included here. Counting them, the shell family is expected to be close to the top ten. It is worth mentioning that shell has always been a stable ranking, unlike some "nouveau riche" languages, such as objective-c, whose popularity is entirely due to the rise of the Apple family, but the craze is likely to come and go faster.

In Github, the largest source code warehouse in the world, the number of shell-related projects accounts for 8%, which is equivalent to Java in the top 5. It can be seen that in actual combat engineering, shell is invincible.

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