# $EPIC: lval.txt,v 1.1 2007/08/06 21:25:50 jnelson Exp $

======Lvalues (aka lvals)======
An lvalue is the token on the left hand side of an assignment operation.
More broadly speaking, an lvalue is a //thing// that may be //assigned to//.

There are several places where you use an lvalue:
| /assign **lval** stuff | Global variable to be assigned a value |
| /local **lval** stuff | Local variable to be assigned a value |
| @ **lval** = stuff | Global variable to be assigned a value |
| /stub assign **lval** filename | Global variable to be loaded on demand |
| $unshift(**lval** stuff) | Prepending to a global variable |
| /unshift **lval** stuff | Prepending to a global variable |
| $push(**lval** stuff) | Appending to a global variable |
| /push **lval** stuff  | Appending to a global variable |
| $shift(**lval** stuff) | Prepending to a global variable |
| /shift **lval** stuff | Prepending to a global variable |
| $pop(**lval** stuff) | Prepending to a global variable |
| /pop **lval** stuff | Prepending to a global variable |
| $aliasctl(SET **lval** ...)  | |
| @ **lval**++ | |
| @ **lval**-- | |
| Any math operator that does an assignment | |
| $splice(**lval** stuff) | |
| $shiftbrace(**lval**) | |
| $sar(r/old/new/**lval**) | |
| $msar(r/old/new/**lval**) | |
| $getopt(...) | |
| /fe (...) **lvals** {...} | |
| /fe :**lval** (...) **lvals** {...} | |
| Arglists | |

======What an lvalue looks like======
An lvalue may be prefixed with zero, one, or two colons:
   * Zero colons means use a local variable if there is one, otherwise use a global variable.
   * One colon means use a local variable only
   * Two colons means use a global variable only

An lvalue contains any number of characters:
   * Any isalpha(3) character
   * Any isdigit(3) character
   * The underscore ("_")
   * The dot (".")

Followed by any number of //array subexpressions//, which are any text 
expression surrounded by square brackets.  There are no restrictions on 
what may be inside an array subexpression.

======Examples:======
	/assign myvar one
	/echo $myvar                  
Will output "one"

	/local myvar two
	/echo $myvar                  
Will output "two" because local variables overrule global variables

	/echo $::myvar
Will output "one" because two colons forces the global variable to be used.

	/assign :othervar one
Creates a //local// variable, because one colon is prefixed.

	/assign ::othervar two
Creates a //global// variable, because two colons are prefixed.

	/assign othervar three
Changes the //local// variable, because local variables overrule global vars.

	@ myvar$testing = [one]
Invalid because  $'s are not allowed in variable names

	@ myvar[$testing] = [one]
Allowed, because array subexpressions can contain any text expression.
Please note that //array subexpressions// are part of the **lval** and
are always treated as text, even in an expression!

	@ myvar.$function() = [one]
Invalid, because no $'s are permitted

	@ myvar[$function()] = [one]
Permitted, because the array subexpression can contain any text.