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Starting the REPL

Launch Nash in interactive mode by running it without arguments: 
nash
You’ll see the welcome banner with your username: 
Nash — Not A Shell  │  logged in as user  │  type help or Ctrl-D to exit

user@nash:/home/user$

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Setting a Custom Username

Use the -U or --user flag to set the session username. This creates a matching home directory and sets all Unix environment variables accordingly: 
nash -U alice
Output: 
Nash — Not A Shell  │  logged in as alice  │  type help or Ctrl-D to exit

alice@nash:/home/alice$
The username affects $USER, $LOGNAME, $HOME, and creates /home/<username> with Desktop/, Documents/, and Downloads/ subdirectories in the VFS.

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Prompt Structure

The Nash prompt follows the classic bash format: 
<username>@nash:<cwd><sigil>
  • username: The session username (set via -U, default: user)
  • cwd: Current working directory (absolute VFS path)
  • sigil: $ for regular users, # for root
user@nash:/home/user$ pwd
/home/user
user@nash:/home/user$ cd /tmp
user@nash:/tmp$

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Command History

Nash uses rustyline for full readline support with command history:
  • ↑/↓ arrows: Navigate through previous commands
  • Ctrl+R: Reverse search through history
  • Tab: Filename completion (if available)

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Viewing History

Use the history builtin to view all executed commands: 
user@nash:/home/user$ echo hello
hello
user@nash:/home/user$ pwd
/home/user
user@nash:/home/user$ ls
Desktop/  Documents/  Downloads/  welcome.txt
user@nash:/home/user$ history
echo hello
pwd
ls
history
Limit output to the last N commands: 
user@nash:/home/user$ history 2
ls
history 2
History is stored in memory and persists throughout the session. It resets when you exit Nash.

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Keyboard Shortcuts

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Ctrl-C: Interrupt

Press Ctrl+C to cancel the current input line without executing it: 
user@nash:/home/user$ echo this will not run^C
user@nash:/home/user$
The ^C is printed and you get a fresh prompt.

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Ctrl-D: Exit

Press Ctrl+D on an empty line to gracefully exit the REPL: 
user@nash:/home/user$ 
logout
This is equivalent to typing exit or quit.

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Exiting the Shell

All three methods exit cleanly: 
user@nash:/home/user$ exit
logout

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Interactive Flags

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Force Interactive Mode

Use -i to force interactive mode even when stdin is not a TTY: 
nash -i
This is useful when piping to Nash but still wanting the REPL: 
echo "pwd" | nash -i

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Starting in a Specific Directory

Use -C or --cwd to override the initial directory: 
nash -C /tmp
Prompt output: 
Nash — Not A Shell  │  logged in as user  │  type help or Ctrl-D to exit

user@nash:/tmp$

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Combining Flags

nash -U alice -C /var/log

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Real-World Examples

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Basic Session

$ nash
Nash — Not A Shell  │  logged in as user  │  type help or Ctrl-D to exit

user@nash:/home/user$ ls
Desktop/  Documents/  Downloads/  welcome.txt
user@nash:/home/user$ cat welcome.txt
Welcome to Nash!
Type 'help' to see available commands.
user@nash:/home/user$ mkdir projects
user@nash:/home/user$ cd projects
user@nash:/home/user/projects$ pwd
/home/user/projects
user@nash:/home/user/projects$ exit
logout

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Using Pipes and Redirections

user@nash:/home/user$ echo "apple\nbanana\napple\ncherry" > fruits.txt
user@nash:/home/user$ cat fruits.txt | sort | uniq
apple
banana
cherry
user@nash:/home/user$ grep "apple" fruits.txt | wc -l
2

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Multi-User Development

$ nash -U developer -C /home/developer
Nash — Not A Shell  │  logged in as developer  │  type help or Ctrl-D to exit

developer@nash:/home/developer$ env | grep USER
USER=developer
LOGNAME=developer
developer@nash:/home/developer$ echo $HOME
/home/developer

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Interactive Detection

Nash automatically detects whether stdin is a TTY. The execution mode follows this priority:
  1. -c CMD → one-shot command
  2. -s → read from stdin
  3. SCRIPT → run script file
  4. -i → forced interactive
  5. stdin is TTY → interactive REPL (default)
  6. stdin is pipe → read from stdin
When Nash detects non-interactive input (pipe or redirect), it skips the welcome banner and prompt, reading commands line-by-line until EOF.

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See Also

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