How do I create a regular expression that detects hexadecimal numbers in a text?
For example, ‘0x0f4’, ‘0acdadecf822eeff32aca5830e438cb54aa722e3’, and ‘8BADF00D’.
This question is related to
regex
It's worth mentioning that detecting an MD5 (which is one of the examples) can be done with:
[0-9a-fA-F]{32}
Another example: Hexadecimal values for css colors start with a pound sign, or hash (#), then six characters that can either be a numeral or a letter between A and F, inclusive.
^#[0-9a-fA-F]{6}
In case you need this within an input where the user can type 0
and 0x
too but not a hex number without the 0x
prefix:
^0?[xX]?[0-9a-fA-F]*$
Not a big deal, but most regex engines support the POSIX character classes, and there's [:xdigit:]
for matching hex characters, which is simpler than the common 0-9a-fA-F
stuff.
So, the regex as requested (ie. with optional 0x
) is: /(0x)?[[:xdigit:]]+/
Just for the record I would specify the following:
/^[xX]?[0-9a-fA-F]{6}$/
Which differs in that it checks that it has to contain the six valid characters and on lowercase or uppercase x in case we have one.
The exact syntax depends on your exact requirements and programming language, but basically:
/[0-9a-fA-F]+/
or more simply, i
makes it case-insensitive.
/[0-9a-f]+/i
If you are lucky enough to be using Ruby, you can do:
/\h+/
EDIT - Steven Schroeder's answer made me realise my understanding of the 0x bit was wrong, so I've updated my suggestions accordingly. If you also want to match 0x, the equivalents are
/0[xX][0-9a-fA-F]+/
/0x[0-9a-f]+/i
/0x[\h]+/i
ADDED MORE - If 0x needs to be optional (as the question implies):
/(0x)?[0-9a-f]+/i
This one makes sure you have no more than three valid pairs:
(([a-fA-F]|[0-9]){2}){3}
Any more or less than three pairs of valid characters fail to match.
This will match with or without 0x
prefix
(?:0[xX])?[0-9a-fA-F]+
If you're using Perl or PHP, you can replace
[0-9a-fA-F]
with:
[[:xdigit:]]
If you are looking for an specific hex character in the middle of the string, you can use "\xhh" where hh is the character in hexadecimal. I've tried and it works. I use framework for C++ Qt but it can solve problems in other cases, depends on the flavor you need to use (php, javascript, python , golang, etc.).
This answer was taken from:http://ult-tex.net/info/perl/
Source: Stackoverflow.com