Why does Powershell -match any string with $null

Question

Found this while debugging a Powershell script.

PS C:\temp> "hello" -match $null  
True

But

> "hello" -eq $null returns False

Why, when using -match, any string will match with $null?

Presumably because the $null regular expression matches anything because it matches against nothing. Similarly you can insert as many ${null}s as you want into the middle of a pattern and not affect its matching because they simply expand to nothing. — Etan Reisner
– Etan Reisner, Commented Apr 14, 2015 at 18:11

Matt · Accepted Answer · 2015-04-14 19:10:23Z

6

I believe this is because the $null gets coerced to an empty string as -match expects a string pattern on the RHS (Right Hand Side). And an empty string will match anything.

edited Apr 14, 2015 at 19:10

Matt

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answered Apr 14, 2015 at 18:13

Keith Hill

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2 Comments

catta Over a year ago

Thanks. Yeah checked and -match with any empty/null variable is True. Empty strings match anything, learn something new everyday :-)

Jeppe Stig Nielsen Over a year ago

This must be correct, for "hello" -match [NullString]::Value explodes with an ArgumentNullException.

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