These definitions are used throughout the remainder of this manual.
A family of open system standards based on Unix. Bash is primarily concerned with the Shell and Utilities portion of the POSIX 1003.1 standard.
A space or tab character.
A command that is implemented internally by the shell itself, rather than by an executable program somewhere in the file system.
token that performs a control function. It is a
or one of the following:
(’, or ‘
The value returned by a command to its caller. The value is restricted to eight bits, so the maximum value is 255.
A unit of text that is the result of one of the shell expansions. After expansion, when executing a command, the resulting fields are used as the command name and arguments.
A string of characters used to identify a file.
A set of processes comprising a pipeline, and any processes descended from it, that are all in the same process group.
A mechanism by which users can selectively stop (suspend) and restart (resume) execution of processes.
A character that, when unquoted, separates words. A metacharacter is
newline, or one of the following characters:
word consisting solely of letters, numbers, and underscores,
and beginning with a letter or underscore.
Names are used as
shell variable and function names.
Also referred to as an
control operator or a
See Redirections, for a list of redirection operators.
Operators contain at least one unquoted
A collection of related processes each having the same process group ID.
process group ID
A unique identifier that represents a
during its lifetime.
word that has a special meaning to the shell. Most reserved
words introduce shell flow control constructs, such as
A synonym for
A mechanism by which a process may be notified by the kernel of an event occurring in the system.
A shell builtin command that has been classified as special by the POSIX standard.
A sequence of characters considered a single unit by the shell.
It is either a
word or an
A sequence of characters treated as a unit by the shell.
Words may not include unquoted