what is linux bash?

Bash (GNU Bourne-Again Shell) is the default shell for many Linux distributions. In fact, there are many shells used in traditional UNIX, such as tcsh, csh, ash, bsh, ksh, etc. The Shell Scripts are generally similar. Once you learn one shell, you will quickly get started with other shells. Most of the time, a Shell Script can usually be used on many kinds of Shells.

bash is the default shell on most Linux systems and Mac OS X. It can run on most Unix-like operating systems. On top of it, it has even been ported to the Cygwin system on Microsoft Windows to implement the POSIX virtual interface of Windows. In addition, it has also been ported to MS-DOS by the DJGPP project.

The command syntax of bash is a superset of the Bourne shell command syntax. Most of the large number of Bourne shell scripts can be executed in bash without modification. Only scripts that use Bourne's special variables or built-in commands need to be modified.

Many of bash’s command syntax comes from Korn shell (ksh) and C shell (csh), such as command line editing, command history, directory stack, $RANDOM and $PPID variables, and POSIX command substitution syntax: $ (...). As an interactive shell, pressing the TAB key can automatically complete the partially entered program name, file name, variable name, etc.

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