Regular expression for a hexadecimal number

Question

How do I create a regular expression that detects hexadecimal numbers in a text   For example     0x0f4        0acdadecf822eeff32aca5830e438cb54aa722e3     and    8BADF00D

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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

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This will match with or without 0x prefix     0 xX    0-9a-fA-F

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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

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How about the following   0 xX  0-9a-fA-F     Matches expression starting with a 0  following by either a lower or uppercase x  followed by one or more characters in the ranges 0-9  or a-f  or A-F

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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

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It s worth mentioning that detecting an MD5  which is one of the examples  can be done with    0-9a-fA-F  32

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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

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If you re using Perl or PHP  you can replace   0-9a-fA-F    with      xdigit

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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

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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

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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

[regex] Regular expression for a hexadecimal number?

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