`Command` Function

Returns the argument portion of the command line used to launch Microsoft Visual Basic or an executable program developed with Visual Basic.

Syntax

Command()

Parameters

None. The Command function takes no arguments.

Return Value

Returns a String containing the command-line arguments passed to the program. If no arguments were passed, returns an empty string ("").

Remarks

The Command function provides access to the command-line arguments that were passed when the application was started. This is commonly used for:

Processing startup parameters
Accepting file paths to open
Enabling debug or special modes
Configuring application behavior at launch

Important Characteristics:

Returns only the arguments, not the executable path
Arguments are returned as a single string
Multiple arguments are separated by spaces (unless quoted)
Quoted strings are preserved but quotes may be included in the result
Leading and trailing spaces are typically trimmed
Returns empty string ("") if no arguments provided
Case is preserved as entered

Command Line Processing

When an application is launched with:

MyApp.exe /debug file.txt "long filename.doc"

Command() returns:

/debug file.txt "long filename.doc"

Examples

Basic Usage

' Get command line arguments
Sub Main()
Dim cmdLine As String
cmdLine = Command()

If cmdLine <> "" Then
MsgBox "Arguments: " & cmdLine
Else
MsgBox "No arguments provided"
End If
End Sub

Processing Switches

Sub Main()
Dim args As String
args = Command()

If InStr(args, "/debug") > 0 Then
App.LogMode = 1  ' Enable debug logging
End If

If InStr(args, "/silent") > 0 Then
App.SilentMode = True
End If
End Sub

Opening a File from Command Line

Sub Main()
Dim filename As String
filename = Trim(Command())

If filename <> "" Then
' Remove quotes if present
If Left(filename, 1) = Chr(34) Then
filename = Mid(filename, 2)
End If
If Right(filename, 1) = Chr(34) Then
filename = Left(filename, Len(filename) - 1)
End If

' Open the file
If Dir(filename) <> "" Then
OpenDocument filename
End If
End If
End Sub

Common Patterns

Parsing Multiple Arguments

Function ParseCommandLine() As Collection
Dim args As New Collection
Dim cmdLine As String
Dim arg As String
Dim pos As Integer
Dim inQuotes As Boolean
Dim i As Integer
Dim ch As String

cmdLine = Trim(Command())
If cmdLine = "" Then Exit Function

arg = ""
inQuotes = False

For i = 1 To Len(cmdLine)
ch = Mid(cmdLine, i, 1)

If ch = Chr(34) Then  ' Quote character
inQuotes = Not inQuotes
ElseIf ch = " " And Not inQuotes Then
If arg <> "" Then
args.Add arg
arg = ""
End If
Else
arg = arg & ch
End If
Next i

If arg <> "" Then args.Add arg

Set ParseCommandLine = args
End Function

Named Parameters

Function GetParameter(paramName As String) As String
Dim cmdLine As String
Dim pos As Integer
Dim endPos As Integer
Dim value As String

cmdLine = " " & Command() & " "
pos = InStr(1, cmdLine, "/" & paramName & ":", vbTextCompare)

If pos = 0 Then
pos = InStr(1, cmdLine, "-" & paramName & ":", vbTextCompare)
End If

If pos > 0 Then
pos = InStr(pos, cmdLine, ":") + 1
endPos = InStr(pos, cmdLine, " ")

If endPos > pos Then
value = Mid(cmdLine, pos, endPos - pos)
GetParameter = Trim(value)
End If
End If
End Function

' Usage:
' MyApp.exe /server:localhost /port:8080
' server = GetParameter("server")  ' Returns "localhost"
' port = GetParameter("port")      ' Returns "8080"

Switch Detection

Function HasSwitch(switchName As String) As Boolean
Dim cmdLine As String
cmdLine = " " & LCase(Command()) & " "

HasSwitch = InStr(cmdLine, " /" & LCase(switchName)) > 0 Or _
InStr(cmdLine, " -" & LCase(switchName)) > 0
End Function

' Usage:
' MyApp.exe /debug /verbose
' If HasSwitch("debug") Then ...

File Association Handler

Sub Main()
Dim filename As String

filename = GetCommandLineFile()

If filename <> "" Then
' Application was launched by double-clicking a file
LoadFile filename
Else
' Application was launched normally
ShowStartupDialog
End If
End Sub

Function GetCommandLineFile() As String
Dim cmdLine As String
cmdLine = Trim(Command())

' Remove surrounding quotes
If Left(cmdLine, 1) = Chr(34) And Right(cmdLine, 1) = Chr(34) Then
cmdLine = Mid(cmdLine, 2, Len(cmdLine) - 2)
End If

' Check if it's a file (not a switch)
If Left(cmdLine, 1) <> "/" And Left(cmdLine, 1) <> "-" Then
If Dir(cmdLine) <> "" Then
GetCommandLineFile = cmdLine
End If
End If
End Function

Configuration File Loading

Sub Main()
Dim configFile As String

configFile = GetParameter("config")

If configFile = "" Then
configFile = App.Path & "\default.cfg"
End If

LoadConfiguration configFile
End Sub

Debug Mode Activation

Public DebugMode As Boolean

Sub Main()
Dim cmdLine As String
cmdLine = LCase(Trim(Command()))

DebugMode = (InStr(cmdLine, "/debug") > 0) Or _
(InStr(cmdLine, "-debug") > 0) Or _
(InStr(cmdLine, "/d") > 0)

If DebugMode Then
MsgBox "Debug mode enabled"
End If
End Sub

Multiple File Processing

Sub Main()
Dim files() As String
Dim i As Integer

files = GetCommandLineFiles()

For i = LBound(files) To UBound(files)
ProcessFile files(i)
Next i
End Sub

Function GetCommandLineFiles() As String()
Dim cmdLine As String
Dim args As Collection
Dim result() As String
Dim i As Integer
Dim count As Integer

Set args = ParseCommandLine()

' Count files (skip switches)
For i = 1 To args.Count
If Left(args(i), 1) <> "/" And Left(args(i), 1) <> "-" Then
count = count + 1
End If
Next i

If count > 0 Then
ReDim result(1 To count)
count = 0

For i = 1 To args.Count
If Left(args(i), 1) <> "/" And Left(args(i), 1) <> "-" Then
count = count + 1
result(count) = args(i)
End If
Next i
End If

GetCommandLineFiles = result
End Function

Automation Mode

Sub Main()
If HasSwitch("auto") Or HasSwitch("batch") Then
' Run in automated mode without UI
RunBatchProcess
End
Else
' Show normal UI
Form1.Show
End If
End Sub

Advanced Usage

Complex Argument Parser

Type CommandLineArg
Name As String
Value As String
IsSwitch As Boolean
End Type

Function ParseAdvancedCommandLine() As Collection
Dim args As New Collection
Dim cmdLine As String
Dim tokens As Collection
Dim i As Integer
Dim token As String
Dim arg As CommandLineArg

cmdLine = Command()
Set tokens = ParseCommandLine()

For i = 1 To tokens.Count
token = tokens(i)

If Left(token, 1) = "/" Or Left(token, 1) = "-" Then
arg.IsSwitch = True

' Remove leading / or -
token = Mid(token, 2)

' Check for name:value format
If InStr(token, ":") > 0 Then
arg.Name = Left(token, InStr(token, ":") - 1)
arg.Value = Mid(token, InStr(token, ":") + 1)
ElseIf InStr(token, "=") > 0 Then
arg.Name = Left(token, InStr(token, "=") - 1)
arg.Value = Mid(token, InStr(token, "=") + 1)
Else
arg.Name = token
arg.Value = "True"
End If
Else
arg.IsSwitch = False
arg.Name = ""
arg.Value = token
End If

args.Add arg
Next i

Set ParseAdvancedCommandLine = args
End Function

Environment Variable Expansion

Function ExpandCommandLine() As String
Dim cmdLine As String
Dim startPos As Integer
Dim endPos As Integer
Dim varName As String
Dim varValue As String

cmdLine = Command()

' Expand %VARIABLE% syntax
Do
startPos = InStr(cmdLine, "%")
If startPos = 0 Then Exit Do

endPos = InStr(startPos + 1, cmdLine, "%")
If endPos = 0 Then Exit Do

varName = Mid(cmdLine, startPos + 1, endPos - startPos - 1)
varValue = Environ(varName)

cmdLine = Left(cmdLine, startPos - 1) & varValue & Mid(cmdLine, endPos + 1)
Loop

ExpandCommandLine = cmdLine
End Function

Help Text Display

Sub Main()
If HasSwitch("?") Or HasSwitch("help") Then
ShowHelp
End
End If

' Normal startup
Form1.Show
End Sub

Sub ShowHelp()
Dim helpText As String

helpText = "MyApp - Command Line Options" & vbCrLf & vbCrLf
helpText = helpText & "/debug        Enable debug mode" & vbCrLf
helpText = helpText & "/config:file  Load configuration from file" & vbCrLf
helpText = helpText & "/silent       Run in silent mode" & vbCrLf
helpText = helpText & "/auto         Run in automated mode" & vbCrLf
helpText = helpText & "/help or /?   Show this help" & vbCrLf

MsgBox helpText, vbInformation
End Sub

Error Handling

Function SafeGetCommand() As String
On Error GoTo ErrorHandler

SafeGetCommand = Command()
Exit Function

ErrorHandler:
' Command() rarely fails, but handle just in case
SafeGetCommand = ""
End Function

Performance Considerations

Command() is a fast function with minimal overhead
Result is cached, so multiple calls don't re-query the OS
Consider caching the result in a module-level variable if used frequently
Parsing complex command lines can be expensive; cache parsed results

Best Practices

Cache the Result

Public g_CommandLine As String

Sub Main()
g_CommandLine = Command()

' Use g_CommandLine throughout the application
If InStr(g_CommandLine, "/debug") > 0 Then
' ...
End If
End Sub

Validate Arguments

Sub Main()
Dim cmdLine As String
cmdLine = Command()

If cmdLine <> "" Then
If Not ValidateCommandLine(cmdLine) Then
MsgBox "Invalid command line arguments", vbCritical
End
End If
End If
End Sub

Use `Sub Main()` for Command Line Apps

Sub Main()
' Process command line before showing any UI
ProcessCommandLine

' Then show UI or continue processing
Form1.Show
End Sub

Limitations

Returns only arguments, not the executable path (use App.Path and App.EXEName instead)
No built-in parsing; returns raw string
Quote handling is not automatic
Limited to approximately 32KB of text on some Windows versions
No standard format for arguments (application must define its own conventions)
Different from C/C++ argv[] which provides separate argument array

App.Path: Returns the path where the application is located
App.EXEName: Returns the executable filename without extension
Environ: Gets environment variable values
Shell: Executes external programs with command lines

Platform Considerations

Windows: Uses GetCommandLine API internally
Command line length limits vary by Windows version
Unicode characters may require special handling
Some special characters may need escaping in batch files

Command Function