Perl Regular Expressions to match a MD5 Hash?
Recently programming in PHP,开发者_开发问答 I thought I had a working Perl regular expression but when I checked it against what I wanted, it didn't work.
What is the right expression to check if something is a MD5 has (32 digit hexadecimal of a-z and 0-9).
Currently, I have /^[a-z0-9]{32}$/i
MD5:
/^[0-9a-f]{32}$/i
SHA-1:
/^[0-9a-f]{40}$/i
MD5 or SHA-1:
/^[0-9a-f]{32}(?:[0-9a-f]{8})?$/i
Also, most hashes are always presented in a lowercase hexadecimal way, so you might wanna consider dropping the i
modifier.
By the way, hexadecimal means base 16:
0 1 2 3 4 5 6 7 8 9 A B C D E F = base 16
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 = base 10
So as you can see it only goes from 0 to F, the same way decimal (or base 10) only goes from 0 to 9.
/^[a-f0-9]{32}$/i
Should work a bit better, since MD5 hashes usually are expressed as hexadecimal numbers.
There is also the POSIX character class xdigit
(see perlreref):
/^[[:xdigit:]]{32}$/
Well, an important point to consider is the fact that $
can match \n
. Therefore:
E:\> perl -e "$x = qq{1\n}; print qq{OK\n} if $x =~ /^1$/" OK
Ooops!
The correct pattern, therefore, is:
/^[[:xdigit:]]{32}\z/
Even easier and faster than RegEx as recommended by PHP Ctype Functions :
function is_md5($s){ return (ctype_xdigit($s) and strlen($s)==32); }
@OP, you might want to use /[a-f0-9]{32,40}/
, this can check for length greater than 32, such as those generated from sha1.
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