Powershell .contains() check without casesensitive

I'm having a larger foreach loop code but need to get below code executed without casesensitive.

Below code snippet returns false, how can I ignore the casesensitive .contains() and the condition as true?

$a='aa0855'
$b='AA0855 Sample'
$b.Contains($a)

Expected value is true. Above code is tried with 2 variables and it returns false.

The .Contains() .NET string method is indeed case-sensitive - invariably in Windows PowerShell, and by default in PowerShell (Core) 7+.

Thus, in PowerShell (Core) 7 you can do:

# PS 7+ only
# -> $true
$a='aa0855'; $b='AA0855 Sample'; $b.Contains($a, 'InvariantCultureIgnoreCase')

The second .Contains() argument is converted to an enumeration value of type StringComparison; InvariantCultureIgnoreCase is the same value that PowerShell's operators use by default, i.e. a case-insensitive comparison that is culture-neutral (i.e. performed in the context of the invariant culture).

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In Windows PowerShell you have two options, using PowerShell operators, which are case-insensitive by default:

• Option A: Use -like, which is wildcard-based:

$a='aa0855'; $b='AA0855 Sample'; $b -like "*$a*" 

If $a contains characters that are metacharacters in the context of a wildcard expression, namely * and ?, and [ / ], escape them, either individually with ` or, more simply, in the entire string with [WildcardPattern]::Escape():

$a='aa0855'; $b='AA0855 Sample'; $b -like ('*{0}*' -f [WildcardPattern]::Escape($a)) 

• Option B: Use -match, which is regex-based:

$a='aa0855'; $b='AA0855 Sample'; $b -match $a

If $a contains characters that are metacharacters in the context of a regex, such as ., they must be escaped, either individually with \, or, more simply, in the entire string with [regex]::Escape():

$a='aa0855'; $b='AA0855 Sample'; $b -match [regex]::Escape($a)

Alternatively, use different / additional .NET APIs that are also available in Windows PowerShell:

• Option C: Look for the index of substring $a in string $b with String.IndexOf(), which can be done case-insensitively; return value -1 indicates that $a isn't a substring of $b:

  $a='aa0855'; $b='AA0855 Sample'
  -1 -ne $b.IndexOf($a, [StringComparison]::InvariantCultureIgnoreCase)
  

  • Note that in this case [StringComparison]::InvariantCultureIgnoreCase, i.e. a value of the exact parameter type must be used to unambiguously target the right method overload; the string shortcut, 'InvariantCultureIgnoreCase', would be ambiguous.

• Option D: Convert both strings to lowercase before using the (single-argument, case-sensitive) .Contains() overload:

  • See js2010's answer.