How do I create a RegEx that matches a string that starts and finishes with a percentage sign?

Question

In a given program, a string should start and finish with a percentage sign and can contain any number of characters in-between. Therefore, the following strings should be valid:

• "%%"
• "% %"
• "%a%"
• "%1%"
• "% a1a %"
• "%%%"

The following strings (for example) would therefore be invalid:

• " %%"
• "%% "
• " % "
• " a%%b "

I am trying to validate these using regular expressions but cannot figure the correct expression. In C# I currently have:

Regex.IsMatch(stringToValidate, "%.*%")

All strings provided above currently match. But I do not want it to match the set of invalid strings.

Answer 1

Use ^%.*%$ with the multi line flag:

https://regex101.com/r/QDX5h3/1

Answer 2

You need to specify an "anchor" (in your case two: start "^" and end "$" of string). Otherwise your pattern will match anywhere inside the complete string and thus " %...% " or abc%...%xx would also match.

Thus, use:

 "^%.*%$"

Answer 3

You can use:

bool foundMatch = Regex.IsMatch(stringToValidate, "^%.*%$");

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