From Bourne shell to Bash
GNU Bash (Bourne-Again SHell) is the default shell on nearly every GNU/Linux system. Developed by Brian Fox for the GNU project starting in 1989, Bash was created as a free replacement for the Unix Bourne shell (sh), maintaining compatibility with the original syntax while adding features borrowed from the Korn shell (ksh) and the C shell (csh).
Version 2.x, currently in use, consolidates a set of features that make Bash a complete tool for both interactive use and scripting: one-dimensional arrays, arithmetic expansion, extended pattern matching, command-line editing with the readline library and history expansion.
Pipelines and composition
The strength of the Unix command line lies in the principle of composition: small, specialised programs connected via pipes (|) that transform data streams in sequence. Bash provides the tools to orchestrate this composition:
- Redirection:
>,>>,<,2>&1to control where standard output, errors and input are directed - Process substitution:
<(command)allows treating a command’s output as a file, enabling comparisons and operations that would otherwise require temporary files - Here documents: inline text blocks passed as input to a command
- Job control: foreground and background process management with
&,fg,bg,jobs
Scripting for administration
A Bash script is an executable text file that combines system commands, control structures (if, for, while, case), variables and functions. For the system administrator, Bash is the daily tool: automated backups, log rotation, user provisioning, service monitoring, application deployment.
Compatibility with the POSIX standard ensures that scripts written with portability in mind work across different shells — sh, dash, ksh — even on non-Linux systems. In practice, however, many scripts take advantage of Bash-specific extensions, and Bash’s ubiquity across GNU/Linux distributions makes the portability concern less pressing.
The command line remains the most powerful and flexible tool for system administration. Graphical interfaces simplify common operations, but for automation, repeatability and fine-grained control, the shell has no equivalent.
Link: gnu.org/software/bash