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VBScript InStr Function

The InStr function returns the position of the first occurrence of one string within another.

The InStr function can return the following values:

If string1 is "" - InStr returns 0
If string1 is Null - InStr returns Null
If string2 is "" - InStr returns start
If string2 is Null - InStr returns Null
If string2 is not found - InStr returns 0
If string2 is found within string1 - InStr returns the position at which match is found
If start > Len(string1) - InStr returns 0

Tip: Also look at the InStrRev function

InStr([start,]string1,string2[,compare])

Parameter	Description
start	Optional. Specifies the starting position for each search. The search begins at the first character position by default. This parameter is required if compare is specified
string1	Required. The string to be searched
string2	Required. The string expression to search for
compare	Optional. Specifies the string comparison to use. Default is 0 Can have one of the following values: 0 = vbBinaryCompare - Perform a binary comparison 1 = vbTextCompare - Perform a textual comparison

Dim txt,pos
txt="This is a beautiful day!"
pos=InStr(txt,"his")
document.write(pos)

Output:

2

Dim txt,pos
txt="This is a beautiful day!"
'A textual comparison starting at position 4
pos=InStr(4,txt,"is",1)
document.write(pos)

Output:

6

Dim txt,pos
txt="This is a beautiful day!"
'A binary comparison starting at position 1
pos=InStr(1,txt,"B",0)
document.write(pos)

Output:

0