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2. Definitions

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.

control operator

A token that performs a control function. It is a newline or one of the following: `||', `&&', `&', `;', `;;', `|', `|&', `(', or `)'.

exit status

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.

job control

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 a blank or one of the following characters: `|', `&', `;', `(', `)', `<', or `>'.


A 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 identifier.


A control operator or a redirection operator. See section Redirections, for a list of redirection operators. Operators contain at least one unquoted metacharacter.

process group

A collection of related processes each having the same process group ID.

process group ID

A unique identifier that represents a process group during its lifetime.

reserved word

A word that has a special meaning to the shell. Most reserved words introduce shell flow control constructs, such as for and while.

return status

A synonym for exit status.


A mechanism by which a process may be notified by the kernel of an event occurring in the system.

special builtin

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 operator.


A sequence of characters treated as a unit by the shell. Words may not include unquoted metacharacters.

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copyright  ©  August 17 2019 sean dreilinger url: https://durak.org/sean/pubs/software/bash-4.1/bashref_4.html