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Having read a number of questions/answers over the past few weeks, I have seen the use of \d in perl regular expressions commented on as incorrect. As in the later versions of perl \d is not the same as [0-9], as \d will represent any Unicode character that has the digit attribute, and that [0-9] represents the characters '0', '1', '2', ..., '9'.
I appreciate that in some contexts [0-9] will be the correct thing to use, and in others \d will be. I was wondering which people feel is the correct default to use?
Personally I find the \d notation very succinct and expressive, whereas in comparison [0-9] is somewhat cumbersome. But I have little experience of doing multi-language code, or rather code for languages that do not fit into the ASCII character range, and therefore may be being naive.
I notice
$find /System/Library/Perl/5.8.8/ -name \*pm | xargs grep '\\d' | wc -l 298 $find /System/Library/Perl/5.8.8/ -name \*pm | xargs grep '\[0-9\]' | wc -l 26 
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As in the later versions of perl \d is not the same as [0-9] , as \d will represent any Unicode character that has the digit attribute, and that [0-9] represents the characters '0', '1', '2', ..., '9'.
The Special Character Classes in Perl are as follows: Digit \d[0-9]: The \d is used to match any digit character and its equivalent to [0-9]. In the regex /\d/ will match a single digit. The \d is standardized to “digit”.
Occurrence Indicators (or Repetition Operators): +: one or more ( 1+ ), e.g., [0-9]+ matches one or more digits such as '123' , '000' . *: zero or more ( 0+ ), e.g., [0-9]* matches zero or more digits. It accepts all those in [0-9]+ plus the empty string.
Decimal digit character: \d \d matches any decimal digit. It is equivalent to the \p{Nd} regular expression pattern, which includes the standard decimal digits 0-9 as well as the decimal digits of a number of other character sets.
It seems to me very dangerous to use \d, It is a poor design decision in the language, as in most cases you want [0-9]. Huffman-coding would dictate the use of \d for ASCII numbers.
Most of the previous posters have already highlighted why you should use [0-9], so let me give you a bit more data:
If I read the unicode charts correctly '۷۰' is a number (70 in indic, don't take my word for it).
Try this:
$ perl -le '$one = chr 0xFF11; print "$one + 1 = ", $one+1;' １ + 1 = 1 Here is a partial list of valid numbers (which may or may not show up properly in your browser, depending on the fonts you use), for each number, only the first of those being interpreted as a number when doing arithmetics with Perl, as shown above:
ZERO: 0٠۰߀०০੦૦୦௦౦೦൦๐໐０ ONE: 1١۱߁१১੧૧୧௧౧೧൧๑໑１ TWO: 2٢۲߂२২੨૨୨௨౨೨൨๒໒２ THREE: 3٣۳߃३৩੩૩୩௩౩೩൩๓໓３ FOUR: 4٤۴߄४৪੪૪୪௪౪೪൪๔໔４ FIVE: 5٥۵߅५৫੫૫୫௫౫೫൫๕໕５ SIX: 6٦۶߆६৬੬૬୬௬౬೬൬๖໖６ SEVEN: 7٧۷߇७৭੭૭୭௭౭೭൭๗໗７ EIGHT: 8٨۸߈८৮੮૮୮௮౮೮൮๘໘８ NINE: 9٩۹߉९৯੯૯୯௯౯೯൯๙໙９�� Are you still not convinced?
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