Bash is a Unix shell and command language written by Brian Fox for the GNU Project as a free software replacement for the Bourne shell. First released in 1989, it has been distributed widely as it is a default shell on the major Linux distributions and OS X.
Bash is a command processor that typically runs in a text window, where the user types commands that cause actions. Bash can also read commands from a file, called a script. Like all Unix shells, it supports filename globbing (wildcard matching), piping, here documents, command substitution, variables and control structures for condition-testing and iteration. The keywords, syntax and other basic features of the language were all copied from sh. Other features, e.g., history, were copied from csh and ksh. Bash is a POSIX shell, but with a number of extensions.
The shell's name is an acronym for Bourne-again shell, punning on the name of the Bourne shell that it replaces and on the term "born again" that denotes spiritual rebirth in contemporary American Christianity.
if [ $days > 365 ]; then echo This is over a year. fi
Alias for used commands
Pattern Matching for filename.
Interactive editing facility using editor.
Home directory can be represented by a tilde sign (~).