使用DOTNET REGEX匹配正确转义的引号

Question

I have a circumstance where I can avoid injecting a user provided string into my PowerShell Code. While I do have code the escape it correctly (duplicating each quote, and powershell with single quoted strings accepts 5 different quote characters including smart quotes, let for now lets just assume it accepts ' What i want to do is have a regex to tell me whether the string is properly escaped, and escaping is done by doubling the quotes so a string as follows

hello ' there

is bad while

hello '' there

is safe

However 3 quotes (or 5 or 7 etc) is also bad so

hello ''' there

is also dangerous

so i'm trying to find a regex that can validate that the string is properly escaped, in that there are no odd numbered single quote patterns.

I know with standard regex counting groups like this is not possible, but with dotnet capture groups i hoped to do something like this.

('\b(?<DEPTH>)|\b'(?<-DEPTH>)|[^']*)*(?(DEPTH)(?!))

but i can't get it to work.

Answer 1

Just because it's you, @klumsy:

"(?ix:                 # ignore whitespace and comments
    ^                  # start at the beginning
    (?(D)              # if 'D' is defined...
        (?<-D>')       #    match a quote and undefine D
        |              # otherwise
        (?:
            (?<D>')    #    match a quote and define D
            |
            [^']       #    or match anything else
            )
    )+                 # as many times as we can
    (?(D)              # if 'D' is STILL defined...
        ($!)           #    then don't match
        |              # otherwise
        [^']*          #    match anything except '
    )$                 # all the way to the end
)"

This will match only those strings which always have the quotes in pairs, but not those strings where a single quote ' or an odd number of quotes ''' appear. Only works with .Net regex, as far as I'm aware.

You can, of course, omit the first and last lines, as long as you remove all whitespace and comments.

Answer 2

Why not simply replace one ' with two '':

> $a = read-host
foo ' bar
> $a
foo ' bar
> $a -replace "'","''"
foo '' bar