Expressions

Terms

A term is an expression that does not include an operator.

Literals

A literal is a term representing a value. Refer to the Types page for details

Identifier

An identifier is a sequence of alphanumeric character or _, not starting with a digit. For example i, _i, _1, i1, a_variable_with_a_long_name3224

Environment variable lookup

To lookup the value of an environment use $identifier. This expression first looks in the current scope to see if there is a variable with the name of identifier and if that is the case it returns the value of the identifier. If not, it will return the value of the environment variable with name identifier. If there is no such environment variable an error is produced.

{
  set ENV1="abc"
  echo $ENV1
} 
echo $ENV1

If this script is run with an environment variable ENV1 set to def, then the script will output

abc
def

Sub expression

A sub expression is just an expression enclosed in (), as in for example (a+4)

This is mostly used when operator precedence is needed to be overwritten, * has higher precedence then +, so (1+2)*3 and 1+2*3 are producing 9 and 7 respectively.

Negated expression

This term has the form !expression and negates the result of expression, in the sense that if expression evaluates to a value that represents true, then !expression will be 1, otherwise it will be 0

An equivalent form is not expression, using not in place of !

Anonymous function

A function construction as described in Types

Operators

Operators work on two terms, for example T1 + T2, here the add operator works on terms T1 and T2. The terms are called operands.

The following set of operators are supported, listed here in precedence order. O

Operator	Description
||	Logical or, if one of the operands evaluates to true, then 1, otherwise 0
&&	logical and, if both operands evaluates to true, then 1 otherwise 0
==	equals, if the operands are identical, then 1 otherwise 0
!=	not equals, if the operands are not identical, then 1 otherwise 0
<	less than, if the left operand is lesser than the right operand, then 1, otherwise 0
>	greater than, if the left operand is greater than the right operand, then 1, otherwise 0
+	For numbers, adds the operands, for lists and strings concatenates the operands
-	Subtracts the numeric operands
*	Multiplies the numeric operands
/	Divides the numeric operands
^	Power, raises the left operand to the power of the right operand

Function call operator

The function call operator invokes a function. The form of this operator is expression(args) where expression evaluates to a function, args is a comma separated list of expression that is taken to be the arguments of the function.

Index operator

The index operator indexes a table or a list and has the form expression[index_expression]. It will return the corresponding element from the evaluation of expression based on the evaluated values of the index_expression.

Infix dot operator

The infix dot operator is a shorthand for indexing tables with the index operator. The form is table_expression.identifier and this is equivalent to table_expression["identifier"]