======Basic Syntax======

xmlsh is derived from a similar syntax as the unix shells (see [[Philosophy Philosophy]]) .  If you are familiar with any of these shell languages (sh,bash,ksh,zsh) you should be right at home. An attempt was made to stay very close to the sh syntax where reasonable, but not all subtlies or features of the unix shells are implemented.  In order to accomidate native XML types and pipelines some deviations and extensions were necessary.  Lastly, as an implementation issue, xmlsh is implemented in java using the [[https://javacc.dev.java.net javacc]] compiler for parsing.  This made support for some of the syntax and features of the C based shells difficult or impossible.  Future work may try to tighten up these issues.

=====Invocation=====

xmlsh can run in 2 modes, interactive and batch.   In interactive mode, a prompt ("$ ") is displayed and in batch mode there is no prompt.  Otherwise they are identical.  Running xmlsh with no arguments starts an interactive shell.  Running with an argument runs in batch mode and invokes the given script.
You can run an xmlsh script by passing it as the first argument, followed by any script arguments
%%(shell)
xmlsh myscript.xsh arg1 arg2
%%

For details on xmlsh invocation and parameters see [[CommandXmlsh xmlsh command]]


=====Environment=====
On invocation, xmlsh inherits the process environment of the caller.  In particular this includes
	- Current Directory 
	- Environment variables
	- Standard ports ( input/output/error )

The shell itself maintains additional environment which is passed to all subshells, but not to external (sub process) commands.
	- Namespaces, including the default namespace (See [[Namespaces]])
	- Declared functions (See [[SyntaxFunction]] )
	- imported modules and packages (See [[Modules]])
	- Shell variables (Environment variables and internal shell variables) (See [[BuiltinVariables]])
	- Positional parameters ($1 ... $n)
	- Shell Options  (-v, -x ...)


=====Running Commands / Basic Syntax =====

On startup, xmlsh reads the standard input (interactive mode) or the script file (batch mode), parses one command at a time and executes it.  The following steps are performed

	- Parse statement.  Statements are parsed using the [[CoreSyntax Core Syntax]].
	- Expand variables.  Variable expansion is performed. See [[Variables]] and [[CoreSyntax]].
	- Variable assignment.  Prefix variable assignment is performed. [[Variables]] and [[CoreSyntax]].
	- IO Redirection. IO redirection (input,output, here documents) [[CommandRedirect]] and [[CoreSyntax]].
	- Command execution.  Commands are executed. [[CommandExecution]]
	- Exceptions raised can be handled with a [[ExceptionHandling try/catch block]].

After the command is executed, then the process repeats.