Can't escape the backslash with regex?

Question

I'm using the following regex

^[a-zA-Z0-9',!;?$^:\/`|~&" @#%*{}()_+.s=-]{1,1000}$

I know it's ugly, but so far it serves its purpose other than the backslash not being allowed as I think it should because it's escaped, I also tried \ instead of \ but same results. Any ideas?

Answer 1

If you're putting this in a string within a program, you may actually need to use four backslashes (because the string parser will remove two of them when "de-escaping" it for the string, and then the regex needs two for an escaped regex backslash).

For instance:

regex("")

is interpreted as...

regex("" [escaped backslash] followed by "" [escaped backslash])

is interpreted as...

regex(\)

is interpreted as a regex that matches a single backslash.

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Depending on the language, you might be able to use a different form of quoting that doesn't parse escape sequences to avoid having to use as many - for instance, in Python:

re.compile(r'\')

The r in front of the quotes makes it a raw string which doesn't parse backslash escapes.