Introduction to the VB.NET ‘Like’ Operator

H o m e

I n t r o d u c t i o n t o t h e V B . N E T ‘ L i k e ’ O p e r a t o r

By Michael McIntyre

The VB.NET ‘Like’ operator compares a string to a pattern returning True if the pattern is found in the string or False if the pattern is not found in the string.

Example One – Introducing the ‘Like’ Operator

In this first example a string containing the upper case F character is compared to a pattern containing the upper case F character.

Dim pattern1 As String = "F"

Console.WriteLine(("F" Like pattern1).ToString)

RESULT: True

Patterns

Example one compared a string to a very simple pattern; a single upper case character.

A pattern can be any String expression conforming to the following pattern-matching conventions.

Characters in pattern	Matches in string
?	Any single character
*	Zero or more characters
#	Any single digit (0–9)
[charlist]	Any single character in charlist
[!charlist]	Any single character not in charlist

Example Two – Using ? in a pattern.

Dim pattern2 As String = "B?t"

Console.WriteLine(("Bat" Like pattern2).ToString)

Console.WriteLine(("Bit" Like pattern2).ToString)

RESULT:

True

A question mark in a pattern matches a single character in a string. In example two the pattern “B?t” will return true when it is compared to any string containing an upper case B followed by any character following by a lower case t. Comparing the words Bit or Bat to the pattern B?t returns True.

Example Three – Using * in a pattern.

Dim pattern3 As String = "Jo*"

Console.WriteLine(("John" Like pattern3).ToString)

Console.WriteLine(("Joan" Like pattern3).ToString)

Console.WriteLine(("JoAnn" Like pattern3).ToString)

RESULT:

True

An asterick in a pattern matches zero or more characters in a string. In example three the pattern “Jo*” will return true when is compared to a string containing an upper case J followed by a lower case 0 followed by 0 or more characters. Comparing the names John, Joan, and JoAnn to the pattern Jo* returns True.

Example Four – Using # in a pattern.

Dim pattern4 As String = "*3##"

Console.WriteLine(("Part-301" Like pattern4).ToString)

Console.WriteLine(("Part-321" Like pattern4).ToString)

RESULT:

True

A pound sign in a pattern matches any single digit in a string. In example four the pattern “*3##” will return true when compared to a string containing 0 or more characters followed by a 3 followed by two digits. Comparing the part identifiers Part-301 and Part-321 to the pattern *3## returns True.

Example Five – Using [charlist] in a pattern.

Dim pattern5 As String = "B[a-f]t"

Console.WriteLine(("Bat" Like pattern5).ToString)

Console.WriteLine(("Bit" Like pattern5).ToString)

RESULT:

True

False

A [charlist] in a pattern is a group of one or more characters (charlist) enclosed in brackets ([ ]) A [charlist] in a pattern can be used to match any single character in string and can include almost any character code, including digits. By using a hyphen (–) to separate the upper and lower bounds of the range, charlist can specify a range of characters. For example, [A-Z] results in a match if the corresponding character position in string contains any uppercase letters in the range A–Z.

In example five the pattern [a-f] will return true when compared to a string containing a character between lower case a and lower case f. Comparing the word Bat to the pattern returns true. Comparing the word Bit returns false because the character i does not fit the pattern.

For more information about the Like operator click here.