A2osX/.Docs/Shell Developers Guide.md

A2osX Shell Developers Guide

One of the most significant parts of A2osX is its shell which can perform both interactive and scripted tasks. With the interactive part of the shell you can perform many common and complex tasks using both built-in (native or internal to shell) and external (BINs or executables) commands. Internal commands include CD (change directory), MD (make directory), DATE, TIME, etc. External commands include CP (copy), RM (remove), CAT (display file contents), TELNET, etc.

It should be noted, that it is possible to create and execute short scripts right on the interactive command line (these are run once and not saved like true scripts). An example

The A2osX Shell (SH)

Variables

Variable overflow strings and ints Ints only no real num it just ignore

The 32-bit int data type can hold integer values in the range of −2,147,483,648 to 2,147,483,647. If you add to or subtract from INTs that would cause a RANGE error, you actually get a result that wraps around the range, so if you add 1 to 2,147,483,647 you will get −2,147,483,648.

Strings can be up to 255 characters in length. Note, like INTs, if you try to store more then 255 chars in a string, you get the same wraparound affect where the first 255 chars are tossed out the string is set to the remaining chars, so if you concatenate 3 strings of 100 chars the resulting string will be the last 45 chars of the 3rd original string.

The Shell Interacting with the Shell. Special Keys

Key	Usage
BACKSPACE	Deletes character under the cursor. Note this key does not exist on Apple keyboards, but may on terminals connected via an SSC or through a Telnet Session
DELETE	Deletes character to left of cursor and moves cursor/rest of line to the left
Control-C	Erases entire command line
Control-D	Exits SHell and if the top most SHell logs you out of your session
Control-Z	Deletes character under the cursor
Up Arrow	Displays previous command from history. Multiple Up Arrows scrolls progressively through history
Down Arrow	Displays next command from history. Multiple Down Arrows scrolls progressively through history
Left Arrow	Moves cursor to the left to edit current command
Right Arrow	Moves cursor to the right to edit current command
Open Apple-0	Switches you to the console display
Open Apple-1 to 4	Switches you to Virtual Terminals 1 through 4 if so configured

Internal Commands

External Commands

Variables

Special Variables

Scripts

Redirection

Advanced Display Techniques

VT100 Codes \f Clear Screen \b backspace \n newline \r return (beginning of line with no new line)

\eM Scroll Screen Down 1 Line \eD Scroll the Screen Up 1 Line \ec Clear Screen

\e[05;15H Move cursor to row 5 and col 15 \e[H Move to home position (0,0) \e[K Clear from cursor to end of line \e[1K Clear from cursor to beginning of line \e[2K Clear line Plus Colors

###Examples

IFTTT Tweet using HTTPGET

Also look at Microsoft Flow and Integromat and Automate.io

where [ exp ] and [ condition ] allow to detail operators....

anywhere you can have [ exp ] you can have ![ exp ] which means NOT exp.

while ![ $total -eq 0 ]
loop

is the same thing as

while [ $total -ne 0 ]
loop

Just like

IF [ A -GT 5 ]
  DO X
ELSE
  DO Y
FI

is the same as

IF ![ A -LE 5 ]
  DO Y
ELSE
  DO X
FI

Notice that the DO X and DO Y logic is swapped between the two cases.

Internal Shell commands:

Name	Status	Comment
<value>	Working	$VAR | string | "string with SPACE" | 123 | -456
<expression>	Working	<value> [<op> <value>] ...
<op>	Working	+ signed int32 add - signed int32 sub * / mod
<condition>	Working	[ -D direxists ] [ -E fileordirexists ] [ -F fileexists ] [ -N $VAR variable is not empty ] [ -Z $VAR variable is empty ] [ string1 = string2 ] [ string1 != string2 ] [ string1 .< string2 ] [ string1 <= string2 ] [ string1 .> string2 ] [ string1 >= string2 ] [ int32 -eq int32 ] [ int32 -ne int32 ] [ int32 -lt int32 ] [ int32 -le int32 ] [ int32 -gt int32 ] [ int32 -ge int32 ]
BREAK	Working	Exit CASE of SWITCH
CALL	Working	CALL function ...
CASE	Working	CASE
CD	Working	CD path or relative path
..	Working	CD ..
DATE	Working
DEFAULT	Working	Default CASE for SWITCH
ECHO	Working	\b,\e,\f,\n,\\ and \% supported -N : Suppress \r\n
ELSE	Working	Optional branch for IF block
END	Working	End of SWITCH Statement
EXIT	Working	exit function, script or shell
FI	Working	Terminator for IF block
FUNCTION	Working	FUNCTION fu
nction_name { <body> }
IF	Working	[ <condition> ] ![ <condition> ]
LOOP	Working	Terminator for WHILE block
MD	Working	MD path or relative path Create a directory
NOHUP	Working	Start a process with PPID=PS0 (Daemon)
PAUSE	Working	Wait until CR
POPD	Working	Restore previously saved working directory
PUSHD	Working	Save actual working directory PUSHD <dir> do also a CD to <dir>
PWD	Working	Print Working Directory
RD	Working	Delete an empty directory
READ	Working	-S : no echo (password) -P : "prompt message" -N maxchar
REN	Working	Rename a file, directory or volume
SET	Working	-X : toggle debug mode -C : toggle Control-C break mode -E : toggle error printing mode -F : delete all declared functions
SHIFT	Working	Remove $1 from cmd line
SLEEP	Working	Wait <count> 10th sec
SWITCH	Working	SWITCH
TIME	Working
WHILE	Working	[ <condition> ]

Shell variables:

Name	Status	Comment
$0	Working	Command Full Path
$1-$9	Working	Arg[n]
$*	Working	All Args
$#	Working	Arg Count
$?	Working	Return Code
$@	Working	Parent PID
	Working	PID
$!	Working	Child PID
$UID	Working	PS Owner UID
$PWD	Working	Working Directory

note : '$VAR' does NOT expand Variable

Shell I/O control/redirection:

Token	Status	Comment
.	Working	use same env
&	Working	start proc
|	Working	pipe
<	Working	StdIn redirection
>	Working	StdOut redirection
>>	Working	Append StdOut
1>>	Working
1>	Working
2>>	Working	StdErr redirection
2>	Working

Stuff to work on

if [] && [] is AND if [] || [] is OR

functions

• DIV/MOD

License

A2osX is licensed under the GNU General Pulic License.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

The full A2osX license can be found Here.

Copyright

Copyright 2015 - 2019, Remy Gibert and the A2osX contributors.