问题
So I am experiencing some inconsistent behavior in my regex
My regex:
(?<=test\\\\)(.*)(?=\",)
The input string:
"test.exe /c echo teststring > \\\\.\\test\\teststring",
When I run this in https://Regex101.com
I get the value teststring however when I run this in F#
Regex.Match(inputString, "(?<=test\\\\)(.*)(?=\",)")
I get \teststring back. My goal is to get just teststring. I'm not sure what I'm doing wrong.
回答1:
I had success using triple quoted strings. Then only the regex escapes need be considered, and not the F# string escapes.
let inputString = """test.exe /c echo teststring > \\\\.\\test\\teststring","""
let x = Regex.Match(inputString, """(?<=test\\\\)(.*)(?=\",)""")
"teststring" comes out
The string in your source comes out as
(?<=test\\)(.*)(?=",)
If you don't want to use triple quotes or verbatim, you will have to write this in F# :
"(?<=test\\\\\\\\)(.*)(?=\\\",)"
This string in F# uses backslashes to escape backslashes and a quote character. There are eight backslashes in a row in one place, and this then becomes four actual backslashes in the string value. There is also this:
\\\"
which translates to one actual \ and one actual " in the actual string value.
So then we end up with a string value of
(?<=test\\\\)(.*)(?=\",)
This then is the actual string value fed to the regex engine. The regex engine, like the F# compiler, also uses the backslash to escape characters. That's why any actual backslash had to be doubled and then doubled again.
来源：https://stackoverflow.com/questions/43262175/regex-is-grabbing-preceding-character