Language Overview

VBScript is a natively implemented Basic-like scripting language that is untyped, Variant-based, and dynamic, supporting procedures (Subs), functions, variable declarations, and global statements, with exception handling using throw/try/catch/finally.

Besides classic VB tokens like Dim, Call, and Set, the syntax includes modern VB.NET-style constructs such as Return, New, and TypeOf/Is, while all variables and parameters are Variants supporting numbers, strings, Booleans, dates, IDispatch objects, and special values Null, Empty, Nothing, True, and False.

Line breaks are significant like in classic Basic, though multiple short statements can share a line using a colon ":"; square-bracket identifiers permit spaces and symbols, useful when interfacing with imported object models.

Global declarations

Global statements can appear anywhere in a unit, even between Sub/Function declarations, and are executed at activation time; declarations define Subs, Functions, and variables with Dim, with optional initializers.

' Variables and routines
Dim X, Y
Dim Z : Z = 7

Sub P(A, B)
  Dim i, j
  Dim k : k = 3
  ShowMessage A + B + F * 3.14
End Sub

Function F()
  F = 7
End Function

' Global statement
ShowMessage "This is a global statement"

Order is flexible: routines and variables may reference each other; Exit exits a routine, and parameters are by value unless semantics specify otherwise for ByRef patterns in host interop.

Conditional Statements (If, Select/Case)

If

If/Then conditionally executes statements; blocks may be a single statement per line or multiple statements when separated by colons or explicit line breaks.

If > 0 Then ShowMessage "X is positive"

If S <> "" Then
  ShowMessage "S is not empty"
Else
  ShowMessage "S is empty"
End If

Select Case

Select Case supports multiple labels per case and an optional Case Else; labels can be strings, numbers, or ranges to simplify multi-branch dispatch.

Select Case x
  Case 0: ShowMessage "Zero"
  Case 1, 3, 5, 7, 9: ShowMessage "Odd"
  Case 2, 4, 6, 8, 10: ShowMessage "Even"
  Case Else: ShowMessage "Too big"
End Select

Loop Statements (For, Do)

For loops iterate over a numeric range; Do While/Loop checks the condition pre- or post-body; Exit exits the current Sub/Function while Continue-like behavior is expressed via control flow patterns.

Dim i

For i = 0 To 10
  ShowMessage i
Next

i = 1
Do While i < 10
  ShowMessage i
  i = i * 2
Loop

i = 1
Do
  ShowMessage i
  i = i * 2
Loop Until i >= 10

Exception Handling Statements (Throw, Try)

Throw

Throw raises an exception object produced by an expression like Exception.Create, assuming availability of the corresponding Delphi exception class in the host environment.

If X > 10 Then
  Throw Exception.Create("X is too big")
End If

Try/Catch/Finally

Try/Catch supports typed catches (On E As T) and a general catch pattern, with Finally ensuring cleanup; rethrow uses a bare Throw within a Catch block.

Try
  DoSomething
Catch
  ShowMessage "Error has occurred."
End Try

Try
  DoSomething
Catch E As EArgumentException
  ShowMessage "Invalid argument"
Catch E As EOutOfMemory
  ShowMessage "Out of memory"
Finally
  Cleanup
End Try

Expressions

Expressions include assignment, calls, property access, arithmetic, logical operators, and literals (numbers, strings, Null/Empty/Nothing/True/False), with support for concatenation and operator precedence.

x = 7: x = -7: x = 7.0
s = "Some string"
s = "This is a string with a quote "" inside"
s = "Line1" & vbCrLf & "Line2"

' Calls & properties
P 5, 7
x = F(3)
s = Application.ActiveForm.Caption

Arrays

VBScript supports single and multi-dimensional arrays; use parentheses in Dim for bounds, default lower bounds apply, and Length/Low/High mirror the host's helpers conceptually.

Dim a(7)          ' 0..7
Dim b(0 To 5)     ' explicit bounds
Dim m(0 To 7, 1 To 3)

Intrinsic Functions

Special branching functions

• Exit
• Break
• Continue

Constants

• Null
• Empty
• Nothing
• True
• False

Functions

• Abs
• ArcTan
• Cos
• Sin
• Ln
• Exp
• Sqr
• Sqrt
• Round
• Trunc
• Int
• Frac
• Random
• Odd
• CompareStr
• CompareText
• AnsiCompareStr
• AnsiCompareText
• AnsiLowerCase
• AnsiUpperCase
• LowerCase
• UpperCase
• Trim
• TrimLeft
• TrimRight
• Copy
• Delete
• Insert
• Pos
• IsValidIdent
• VarIsNull
• IntToStr
• IntToHex
• FloatToStr
• VarToStr
• Format
• FormatFloat
• FormatDateTime
• Date
• Time
• Now
• DateToStr
• TimeToStr
• DateTimeToStr
• StrToDate
• StrToTime
• StrToDateTime
• DecodeDate
• DecodeTime
• EncodeDate
• EncodeTime
• DayOfWeek
• IsLeapYear
• IncMonth
• StrToFloat
• StrToInt
• StrToIntDef
• Include
• Exclude
• High
• Low
• Length
• Ord
• Assigned
• Inc
• Dec
• Chr
• ShowMessage
• InputQuery
• Beep
• CreateOleObject
• GetActiveOleObject

BNF Syntax

The grammar summary outlines units, declarations, statements, expressions, arrays, and operators accepted by VBScript, reflecting its Basic-style syntax and precedence.

<Unit> ::= {<GlobalStmt> | <SubDecl> | <FuncDecl>}
<GlobalStmt> ::= <Statement> NEWLINE
<SubDecl> ::= Sub <Identifier>  NEWLINE <StmtBlock> End Sub
<FuncDecl> ::= Function <Identifier>  NEWLINE <StmtBlock> End Function
<Params> ::= <Identifier> {"," <Identifier>}
<StmtBlock> ::= {<Statement> NEWLINE}
<Statement> ::= <Assignment> | <Call> | <IfStmt> | <SelectStmt> | <ForStmt> | <DoStmt> | <TryStmt> | <ThrowStmt>
<Assignment> ::= <Designator> "=" <Expression>
<IfStmt> ::= If <Expression> Then <StmtBlock>  End If
<SelectStmt> ::= Select Case <Expression> NEWLINE {Case <CaseLabelList> ":" <StmtBlock>}  End Select
<ForStmt> ::= For <Identifier> "=" <Expression> To <Expression> NEWLINE <StmtBlock> Next
<DoStmt> ::= Do  NEWLINE <StmtBlock> Loop 
<TryStmt> ::= Try NEWLINE <StmtBlock> {Catch  NEWLINE <StmtBlock>}  End Try
<ThrowStmt> ::= Throw <Expression>
<Expression> ::= ...  ; literals, calls, properties, operators
<ArrayDecl> ::= Dim <Identifier> "(" <Bounds> {"," <Bounds>} ")"
<Bounds> ::= INT | INT To INT