GNU bash

Bash Reference Manual

Reference Documentation for Bash

Edition (4).3, for Bash Version (4).3.

February (2014)

Chet Ramey, Case Western Reserve University

Brian Fox, Free Software Foundation

This text is a brief description of the features that are present in the Bash shell (version (4).3, 2 February (2014)).

This is Edition (4).3, last updated (2) February (2014), of The GNU Bash Reference Manual, for Bash, Version (4).3.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version (1).3 or any later version published by the Free Software Foundation. A copy of the license is included in the section entitled “GNU Free Documentation License”. The ePub version is made freely available by atog.nl.

Table of Contents

Introduction (1)

1.1

What is Bash? (1)

1.2

What is a shell? (1)

Definitions (3)

Basic Shell Features (5)

3.1

Shell Syntax (5)

3.1.1

Shell Operation (5)

3.1.2

Quoting (6)

3.1.2.1

Escape Character (6)

3.1.2.2

Single Quotes (6)

3.1.2.3

Double Quotes (6)

3.1.2.4

ANSI-C Quoting (6)

3.1.2.5

Locale-Specific Translation (7)

3.1.3

Comments (7)

3.2

Shell Commands (8)

3.2.1

Simple Commands (8)

3.2.2

Pipelines (8)

3.2.3

Lists of Commands (9)

3.2.4

Compound Commands (9)

3.2.4.1

Looping Constructs (10)

3.2.4.2

Conditional Constructs (10)

3.2.4.3

Grouping Commands (14)

3.2.5

Coprocesses (15)

3.2.6

GNU Parallel (15)

3.3

Shell Functions (17)

3.4

Shell Parameters (18)

3.4.1

Positional Parameters (19)

3.4.2

Special Parameters (20)

3.5

Shell Expansions (21)

3.5.1

Brace Expansion (21)

3.5.2

Tilde Expansion (22)

3.5.3

Shell Parameter Expansion (23)

3.5.4

Command Substitution (28)

3.5.5

Arithmetic Expansion (29)

3.5.6

Process Substitution (29)

3.5.7

Word Splitting (29)

3.5.8

Filename Expansion (30)

3.5.8.1

Pattern Matching (30)

3.5.9

Quote Removal (31)

3.6

Redirections (31)

3.6.1

Redirecting Input (33)

3.6.2

Redirecting Output (33)

3.6.3

Appending Redirected Output (33)

3.6.4

Redirecting Standard Output and Standard Error (33)

3.6.5

Appending Standard Output and Standard Error (34)

3.6.6

Here Documents (34)

3.6.7

Here Strings (34)

3.6.8

Duplicating File Descriptors (34)

3.6.9

Moving File Descriptors (35)

3.6.10

Opening File Descriptors for Reading and Writing (35)

3.7

Executing Commands (35)

3.7.1

Simple Command Expansion (35)

3.7.2

Command Search and Execution (36)

3.7.3

Command Execution Environment (36)

3.7.4

Environment (37)

3.7.5

Exit Status (38)

3.7.6

Signals (38)

3.8

Shell Scripts (39)

Shell Builtin Commands (41)

4.1

Bourne Shell Builtins (41)

4.2

Bash Builtin Commands (48)

4.3

Modifying Shell Behavior (58)

4.3.1

The Set Builtin (58)

4.3.2

The Shopt Builtin (62)

4.4

Special Builtins (68)

Shell Variables (69)

5.1

Bourne Shell Variables (69)

5.2

Bash Variables (69)

Bash Features (80)

6.1

Invoking Bash (80)

6.2

Bash Startup Files (82)

6.3

Interactive Shells (83)

6.3.1

What is an Interactive Shell? (83)

6.3.2

Is this Shell Interactive? (84)

6.3.3

Interactive Shell Behavior (84)

6.4

Bash Conditional Expressions (85)

6.5

Shell Arithmetic (87)

6.6

Aliases (88)

6.7

Arrays (89)

6.8

The Directory Stack (90)

6.8.1

Directory Stack Builtins (90)

6.9

Controlling the Prompt (92)

6.10

The Restricted Shell (93)

6.11

Bash POSIX Mode (94)

iii

Job Control (97)

7.1

Job Control Basics (97)

7.2

Job Control Builtins (98)

7.3

Job Control Variables (100)

Command Line Editing (101)

8.1

Introduction to Line Editing (101)

8.2

Readline Interaction (101)

8.2.1

Readline Bare Essentials (102)

8.2.2

Readline Movement Commands (102)

8.2.3

Readline Killing Commands (103)

8.2.4

Readline Arguments (103)

8.2.5

Searching for Commands in the History (103)

8.3

Readline Init File (104)

8.3.1

Readline Init File Syntax (104)

8.3.2

Conditional Init Constructs (111)

8.3.3

Sample Init File (112)

8.4

Bindable Readline Commands (115)

8.4.1

Commands For Moving (115)

8.4.2

Commands For Manipulating The History (116)

8.4.3

Commands For Changing Text (117)

8.4.4

Killing And Yanking (118)

8.4.5

Specifying Numeric Arguments (119)

8.4.6

Letting Readline Type For You (120)

8.4.7

Keyboard Macros (121)

8.4.8

Some Miscellaneous Commands (122)

8.5

Readline vi Mode (124)

8.6

Programmable Completion (124)

8.7

Programmable Completion Builtins (126)

8.8

A Programmable Completion Example (130)

Using History Interactively (133)

9.1

Bash History Facilities (133)

9.2

Bash History Builtins (133)

9.3

History Expansion (135)

9.3.1

Event Designators (135)

9.3.2

Word Designators (136)

9.3.3

Modifiers (137)

Installing Bash (138)

10.1

Basic Installation (138)

10.2

Compilers and Options (139)

10.3

Compiling For Multiple Architectures (139)

10.4

Installation Names (139)

10.5

Specifying the System Type (139)

10.6

Sharing Defaults (140)

10.7

Operation Controls (140)

10.8

Optional Features (140)

Appendix A

Reporting Bugs (145)

Appendix B

Major Differences From The

Bourne Shell (146)

B.1

Implementation Differences From The SVR4.2 Shell (150)

Appendix C

GNU Free Documentation License (152)

Appendix D

Indexes (160)

D.1

Index of Shell Builtin Commands (160)

D.2

Index of Shell Reserved Words (161)

D.3

Parameter and Variable Index (161)

D.4

Function Index (163)

D.5

Concept Index (165)