Comparison operators in VB.NET

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Comparison operators
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In computers, a comparison always involves taking two objects or values and testing their relationship to one another. You might be testing to see if they re equal, or to see if one is greater than another, or if one of them matches a text pattern of some kind. You indicate the kind of relationship you want to test by using a comparison operator. The result of the test is always a Boolean value: True or False. In other words, either the tested relationship is as you specified, or it isn t. PowerShell uses the following comparison operators. Note that, when comparing text strings, these aren t case-sensitive. That means an uppercase letter is seen as equal to a lowercase letter.
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Comparison operators
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-eq Equality, as in 5 -eq 5 (which is True) or "hello" -eq "help" (which is False) -ne Not equal to, as in 10 -ne 5 (which is True) or "help" -ne "help" (which is False, because they are, in fact, equal, and we were testing to see if
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they were inequal) -ge and -le Greater than or equal to, and less than or equal to, as in 10 -ge 5 (True) or Get-Date -le '2012-12-02' (which will depend on when you run this, and shows how dates can be compared in this fashion) -gt and -lt Greater than and less than, as in 10 -lt 10 (False) or 100 -gt 10 (True)
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For string comparisons, you can use a separate set of operators that are case-sensitive, if needed: -ceq, -cne, -cgt, -clt, -cge, -cle. If you want to compare more than one thing at once, you can use the Boolean operators -and and -or. Each of those takes a subexpression on either side, and I usually enclose them in parentheses to make the line clearer to read:
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(5 -gt 10) -and (10 -gt 100) is False, because one or both subexpressions were False. (5 -gt 10) -or (10 -lt 100) is True, because at least one subexpression was True.
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In addition, the Boolean -not operator simply reverses True and False. This can be useful when you re dealing with a variable or a property that already contains True or False, and you want to test for the opposite condition. For example, if I wanted to test whether a process was not responding, I could do this (I m going to use $_ as a placeholder for a process object):
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$_.Responding -eq $False
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Windows PowerShell defines $False and $True to represent the False and True Boolean values. Another way to write that comparison would be as follows:
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-not $_.Responding
Because Responding normally contains True or False, the -not will reverse False to True. So if the process isn t responding (meaning Responding is False), my comparison will return True, indicating that the process is not responding. I prefer the second technique because it reads, in English, more like what I m actually testing for: I want to see if the process is not responding. You ll sometimes see the -not operator abbreviated as an exclamation mark (!). There are a couple of other comparison operators that are especially useful when you need to compare strings of text:
-like accepts * as a wildcard, so you can compare to see if "Hello" -like "*ll*" (that would be True). -notlike is the reverse, and both are caseinsensitive; use -clike and -cnotlike for case-sensitive comparisons.
Filtering and comparisons
-match makes a comparison between a string of text and a regular expression pattern. -notmatch is its logical opposite, and as you might expect, -cmatch and -cnotmatch provide case-sensitive versions. Regular expressions are beyond the
scope of what we ll cover in this book. The neat thing about the shell is that you can test almost all of these right at the command line (the exception is the one where I used the $_ placeholder it won t work by itself, but you ll see where it will work in just a moment).
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