- defined by the POSIX standard)[/link]
- anacron, Scheduling Commands to run in the background
- analyze, Miscellaneous
- AND, Performing more than one command
- antiword, Text Conversion/Filter Tools
- antiword homepage, Text Conversion/Filter Tools
- append, Moving around the filesystem , Finding information about the system , File Permissions
- appendix, Introduction , Who would want to read this guide?
- application, The Unix Tools Philosophy , Working with files and folders
- apply, Controlling Processes
- apropos, Help
- apt-get, RPM: Redhat Package Management System
- archive, Internet Specific Commands , Archiving Files , Compression
- archived, tar (tape archiver)
- archives, Compression
- archiving, Archiving Files
- argument, Working with files and folders , Mass Rename/copy/link Tools , Text Information Tools , Text manipulation tools , Internet Specific Commands , Scheduling Commands to run in the background , Miscellaneous
- arguments, The command-line history , Working with files and folders
- arranged, Graphics tools (command line based)
- arrow, The command-line history
- arrow keys, The command-line history
- art, Conversion tools
- article, Contributors
- ASCII, The Unix Tools Philosophy , Moving around the filesystem , Working with files and folders , Text Conversion/Filter Tools , Conversion tools
- aspell, Text manipulation tools
- assign, Controlling Processes
- assist,

