Features
The Bash command syntax is a superset of the Bourne shell command syntax. The vast majority of Bourne shell scripts can be executed by Bash without modification, with the exception of Bourne shell scripts stumbling into fringe syntax behavior interpreted differently in Bash or attempting to run a system command matching a newer Bash builtin, etc. Bash command syntax includes ideas drawn from the Korn shell (ksh) and the C shell (csh) such as command line editing, command history, the directory stack, the $RANDOM and $PPID variables, and POSIX command substitution syntax $(…). When used as an interactive command shell and pressing the tab key, Bash automatically uses command line completion to match partly typed program names, filenames and variable names. The Bash command-line completion system is very flexible and customizable, and is often packaged with functions that complete arguments and filenames for specific programs and tasks.
Bash's syntax has many extensions which the Bourne shell lacks. Bash can perform integer calculations without spawning external processes, unlike the Bourne shell. Bash uses the ((…)) command and the $((…)) variable syntax for this purpose. Bash syntax simplifies I/O redirection in ways that are not possible in the traditional Bourne shell. For example, Bash can redirect standard output (stdout) and standard error (stderr) at the same time using the &> operator. This is simpler to type than the Bourne shell equivalent 'command > file 2>&1'. Bash supports process substitution using the <(command) syntax, which substitutes the output of (or input to) a command where a filename is normally used.
When using the 'function' keyword, Bash function declarations are not compatible with Bourne/Korn/POSIX scripts (the Korn shell has the same problem when using 'function'), but Bash accepts the same function declaration syntax as the Bourne and Korn shells, and is POSIX conformant. Due to these and other differences, Bash shell scripts are rarely runnable under the Bourne or Korn shell interpreters unless deliberately written with that compatibility in mind, which is becoming less common as Linux becomes more widespread. But in POSIX mode, Bash conformance with POSIX is nearly perfect.
Bash supports here documents just as the Bourne shell always has. In addition, since version 2.05b Bash can redirect standard input (stdin) from a "here string" using the <<< operator.
Bash 3.0 supports in-process regular expression matching using a syntax reminiscent of Perl.
Bash 4.0 introduced support for associative arrays. Associative arrays allow a fake support for multi-dimensional (indexed) arrays, in a similar way to AWK:
declare -A a # declare an associative array 'a' faking a bi-dimensional indexed array i=1; j=2 # initialize some indices a=5 # associate value "5" to key "$i,$j" (i.e. "1,2") echo ${a} # print the stored value at key "$i,$j"Read more about this topic: Bash (Unix Shell)
Famous quotes containing the word features:
“Art is the child of Nature; yes,
Her darling child, in whom we trace
The features of the mother’s face,
Her aspect and her attitude.”
—Henry Wadsworth Longfellow (1807–1882)
“All visible objects, man, are but as pasteboard masks. But in each event—in the living act, the undoubted deed—there, some unknown but still reasoning thing puts forth the mouldings of its features from behind the unreasoning mask. If man will strike, strike through the mask!”
—Herman Melville (1819–1891)