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Shell brief introduction

1.Bash production

bash is a Unix shell written for the GNU project. Its name is a series of abbreviations: Bourne-Again SHell -a pun on Bourne shell (sh)(Bourne again / born again). The Bourne shell was an early and important shell, and Bash is the default Shell for many Linux distributions. It was written by Stephen Bourne around 1978 and released with Version 7 Unix. bash was created in 1987 by Brian Fox. In 1990, Chet Ramey became a major defender.

bash is the default shell for most Linux systems and Mac OS X v10.4, and runs on most Unix-style operating systems, even ported to Cygwin on Microsoft Windows to implement Windows 'POSIX virtual interface. It was also ported to MS-DOS by the DJGPP project.

In fact, there are many traditional UNIX shells, such as tcsh, csh, ash, bsh, ksh, etc. Shell Script is roughly the same, when you learn one Shell, other shells will soon learn, most of the time, a Shell Script can usually be used on many shells.

bash is the default shell for most Linux systems and Mac OS X, and runs on most Unix-like operating systems, and has even been ported to Cygwin on Microsoft Windows to implement Windows POSIX virtual interfaces. It was also ported to MS-DOS by the DJGPP project.

bash command syntax is a superset of Bourne shell command syntax. Most of Bourne's vast number of shell scripts can be executed in bash without modification, except for scripts that reference Bourne special variables or use Bourne's built-in commands. bash's command syntax comes from many sources such as the Korn shell (ksh) and C shell (csh), such as command-line editing, command history, directory stacks,$RANDOM and $PPID variables, and POSIX's command substitution syntax: $(...). As an interactive shell, pressing TAB automatically completes partially typed program names, file names, variable names, etc.

Shell system diagram

II. Parameter Description Edit-c String: If-c parameter is used, bash reads the command from the string, and if there are variables after the string, it is set to the position parameter starting from $0. - i: If-i is used, bash is interactive. - s: With the-s argument, bash reads the command from standard input (after executing the command with-c). until you type exit. - : A single sign indicates that the parameter has been executed, and blocks all subsequent parameters, and all subsequent variables are treated as file names. - norc: If bash is interactive, the personal initialization file is not executed: -/.bashrc, if bash is run as sh, this parameter defaults to off. - noprofile: does not execute system-wide startup files/etc/profile nor personal startup files-/.bash_profile, -/.bash_login or-/.profile, which are used as startup files by default when bash is used as a login shell. -- file name: If bash is interactive, this file is used as bash's startup file. Replace-/.bashrc. - version: Displays the version number of this bash at the beginning of the bash. - quiet: does not display version numbers and other information, this is the default. - login: Activate bash, masquerading as login shell. - nobraceexpansion: does not perform brace expansion. - nolineediting: Do not use GNU's readline library to read commands in interactive mode. Command line editing is disabled. - posix: change bash behavior to conform to the criteria specified in Posix 1003.2.

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