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% NESSIE(1) % Tore Bergebakken % November 2020

NAME

ne[sh]ie – the absurdly stupid shell

SYNOPSIS

nessie [-d|--debug] [-h|--help] [-c|--command COMMAND] [FILE]

DESCRIPTION

nessie is a simple Linux shell developed as a hobby project. It is not intended to replace well-known, fully-featured shells like bash in any way. That being said, it does have enough functionality to be somewhat useful.

OPTIONS

FILE : Script file that Nessie should execute. Overriden by -c.

-h, --help : Display a friendly help message.

-c, --command : Execute a command, or a set of commands, specified as option parameter

-d, --debug : Run the shell in debug mode – Nessie will print extra information

SYNTAX

Nessie's syntax should be familiar to anyone with some experience using standard UNIX shells. It is meant to follow a tiny subset of Bourne Shell syntax.

The grammar can be summarized as follows:

LINE      := STATEMENT [; STATEMENT]* [# COMMENT]
STATEMENT := COMMAND
           | COMMAND && STATEMENT
           | COMMAND || STATEMENT
COMMAND   := PROG [ARG]* [| COMMAND]*
PROG, ARG := TOKEN
           | "TOKEN [TOKEN]*"
           | 'WORD [WORD]*'
TOKEN     := VARIABLE
           | WORD
VARIABLE  := $[A-Za-z0-9]+
WORD      := <just continuous text>
COMMENT   := <any text following a #>

Command : An exectuable file in your PATH, or a builtin. Takes some arguments and/or input, does whatever it is supposed to and returns an exit code.

Pipeline : The output of one command can be piped into another – that is, whatever the command would print if you ran it by itself, will become the input to the command after the | sign.

Short-circuiting : Nessie supports conditional execution, also known as short-circuiting, with the && and || operators, which correspond to logical AND and OR. A command that exits with status code 0, triggers the next &&. A command that exits with a nonzero status code, triggers the next ||.

Variables : Variables, which are alphanumeric strings following a dollar sign ($), will expand to whatever their value is. Their values can be set outside of Nessie, and passed as environment variables to commands executed by Nessie. Use the let builtin to set them.

Comment : Anything that folows a # that is not within a string, is ignored. This is typically used to add informational text to scripts.

BUILTINS

cd : Change directory. Usage: cd /usr/share/

let : Set an environment variable. Usage: let fruit apple

true : Returns exit code 0. Usage: true && echo "success!"

false : Returns exit code 1. Usage: false || echo "failure..."

history : Prints a list of previously executed commands.

help : Print some useful information. You'd get more out of reading this manual, though.

exit : Exit the shell. Alias: q

EXAMPLES

  1. Execute a shell command from a string:

    nessie -c "true && false || echo whatever | tr a o"

  2. Start an interactive session

    nessie

  3. Run a script file

    nessie script.sh

  4. Run a script/command from standard input

    echo "echo something" | nessie

  5. Use an environment variable

    var="Hello World" nessie -c 'echo "$var, I am a shell"'