Linux Command Line and Shell Scripting Bible, 4th Edition

APPENDIX AQuick Guide to Bash Commands

IN THIS APPENDIX

• Reviewing built‐in commands
• Looking at common Bash commands
• Assessing environment variables

As you've seen throughout this book, the Bash shell contains lots of features and thus has lots of commands available. This appendix provides a concise guide to allow you to quickly look up a feature or command that you can use from the Bash command line or from a Bash shell script.

Reviewing Built‐In Commands

The Bash shell includes many popular commands built into the shell. You can use these commands to achieve faster processing times. Table A.1 shows the built‐in commands available directly from the Bash shell.

TABLE A.1 Bash Built‐In Commands

Command	Description
&	Starts a job in background mode
(( x ))	Evaluates the x mathematical expression
not:	Reads and executes commands from a designated file in the current shell
:	Does nothing, and always exits successfully
[ t ]	Evaluates the t conditional expression
[[ e ]]	Evaluates the e conditional expression
alias	Defines an alias for the specified command
bg	Resumes a job in background mode
bind	Binds a keyboard sequence to a readline function or macro
break	Exits from a for , while , select , or until loop
builtin	Executes the specified shell built‐in command
caller	Returns the context of any active subroutine call
case	Selectively executes commands based on pattern
cd	Changes the current directory to the ...