X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlre.pod;h=02dd2cda5d8260ce0421f39218d9070d90372e7c;hb=a0acbdc36d211b2eba42328df555d9ec49fa4cd4;hp=2db4139c30ddb7095ed43d12eeb14628704d3241;hpb=92d29cee5ff815b05b81b877528e4c77e73881c9;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlre.pod b/pod/perlre.pod index 2db4139..02dd2cd 100644 --- a/pod/perlre.pod +++ b/pod/perlre.pod @@ -40,7 +40,7 @@ is, no matter what C<$*> contains, C without C will force "^" to match only at the beginning of the string and "$" to match only at the end (or just before a newline at the end) of the string. Together, as /ms, they let the "." match any character whatsoever, -while yet allowing "^" and "$" to match, respectively, just after +while still allowing "^" and "$" to match, respectively, just after and just before newlines within the string. =item x @@ -169,7 +169,7 @@ You'll need to write something like C. In addition, Perl defines the following: \w Match a "word" character (alphanumeric plus "_") - \W Match a non-word character + \W Match a non-"word" character \s Match a whitespace character \S Match a non-whitespace character \d Match a digit character @@ -179,8 +179,9 @@ In addition, Perl defines the following: \X Match eXtended Unicode "combining character sequence", equivalent to C<(?:\PM\pM*)> \C Match a single C char (octet) even under utf8. + (Currently this does not work correctly.) -A C<\w> matches a single alphanumeric character, not a whole word. +A C<\w> matches a single alphanumeric character or C<_>, not a whole word. Use C<\w+> to match a string of Perl-identifier characters (which isn't the same as matching an English word). If C is in effect, the list of alphabetic characters generated by C<\w> is taken from the @@ -199,38 +200,47 @@ equivalents (if available) are as follows: alpha alnum ascii + blank [1] cntrl digit \d graph lower print punct - space \s + space \s [2] upper - word \w + word \w [3] xdigit + [1] A GNU extension equivalent to C<[ \t]>, `all horizontal whitespace'. + [2] Not I to C<\s> since the C<[[:space:]]> includes + also the (very rare) `vertical tabulator', "\ck", chr(11). + [3] A Perl extension. + For example use C<[:upper:]> to match all the uppercase characters. -Note that the C<[]> are part of the C<[::]> construct, not part of the whole -character class. For example: +Note that the C<[]> are part of the C<[::]> construct, not part of the +whole character class. For example: [01[:alpha:]%] -matches one, zero, any alphabetic character, and the percentage sign. +matches zero, one, any alphabetic character, and the percentage sign. If the C pragma is used, the following equivalences to Unicode -\p{} constructs hold: +\p{} constructs and equivalent backslash character classes (if available), +will hold: alpha IsAlpha alnum IsAlnum ascii IsASCII + blank IsSpace cntrl IsCntrl - digit IsDigit + digit IsDigit \d graph IsGraph lower IsLower print IsPrint punct IsPunct space IsSpace + IsSpacePerl \s upper IsUpper word IsWord xdigit IsXDigit @@ -238,8 +248,8 @@ If the C pragma is used, the following equivalences to Unicode For example C<[:lower:]> and C<\p{IsLower}> are equivalent. If the C pragma is not used but the C pragma is, the -classes correlate with the isalpha(3) interface (except for `word', -which is a Perl extension, mirroring C<\w>). +classes correlate with the usual isalpha(3) interface (except for +`word' and `blank'). The assumedly non-obviously named classes are: @@ -250,23 +260,24 @@ The assumedly non-obviously named classes are: Any control character. Usually characters that don't produce output as such but instead control the terminal somehow: for example newline and backspace are control characters. All characters with ord() less than -32 are most often classified as control characters. +32 are most often classified as control characters (assuming ASCII, +the ISO Latin character sets, and Unicode). =item graph -Any alphanumeric or punctuation character. +Any alphanumeric or punctuation (special) character. =item print -Any alphanumeric or punctuation character or space. +Any alphanumeric or punctuation (special) character or space. =item punct -Any punctuation character. +Any punctuation (special) character. =item xdigit -Any hexadecimal digit. Though this may feel silly (/0-9a-f/i would +Any hexadecimal digit. Though this may feel silly ([0-9A-Fa-f] would work just fine) it is included for completeness. =back @@ -323,12 +334,14 @@ I. There is no limit to the number of captured substrings that you may use. However Perl also uses \10, \11, etc. as aliases for \010, -\011, etc. (Recall that 0 means octal, so \011 is the 9'th ASCII -character, a tab.) Perl resolves this ambiguity by interpreting -\10 as a backreference only if at least 10 left parentheses have -opened before it. Likewise \11 is a backreference only if at least -11 left parentheses have opened before it. And so on. \1 through -\9 are always interpreted as backreferences." +\011, etc. (Recall that 0 means octal, so \011 is the character at +number 9 in your coded character set; which would be the 10th character, +a horizontal tab under ASCII.) Perl resolves this +ambiguity by interpreting \10 as a backreference only if at least 10 +left parentheses have opened before it. Likewise \11 is a +backreference only if at least 11 left parentheses have opened +before it. And so on. \1 through \9 are always interpreted as +backreferences. Examples: @@ -352,7 +365,7 @@ everything before the matched string. And C<$'> returns everything after the matched string. The numbered variables ($1, $2, $3, etc.) and the related punctuation -set (C<<$+>, C<$&>, C<$`>, and C<$'>) are all dynamically scoped +set (C<$+>, C<$&>, C<$`>, and C<$'>) are all dynamically scoped until the end of the enclosing block or until the next successful match, whichever comes first. (See L.) @@ -377,10 +390,11 @@ that looks like \\, \(, \), \<, \>, \{, or \} is always interpreted as a literal character, not a metacharacter. This was once used in a common idiom to disable or quote the special meanings of regular expression metacharacters in a string that you want to -use for a pattern. Simply quote all non-alphanumeric characters: +use for a pattern. Simply quote all non-"word" characters: $pattern =~ s/(\W)/\\$1/g; +(If C is set, then this depends on the current locale.) Today it is more common to use the quotemeta() function or the C<\Q> metaquoting escape sequence to disable all metacharacters' special meanings like this: @@ -901,10 +915,14 @@ ways they can use backtracking to try match. For example, without internal optimizations done by the regular expression engine, this will take a painfully long time to run: - 'aaaaaaaaaaaa' =~ /((a{0,5}){0,5}){0,5}[c]/ + 'aaaaaaaaaaaa' =~ /((a{0,5}){0,5})*[c]/ -And if you used C<*>'s instead of limiting it to 0 through 5 matches, -then it would take forever--or until you ran out of stack space. +And if you used C<*>'s in the internal groups instead of limiting them +to 0 through 5 matches, then it would take forever--or until you ran +out of stack space. Moreover, these internal optimizations are not +always applicable. For example, if you put C<{0,5}> instead of C<*> +on the external group, no current optimization is applicable, and the +match takes a long time to finish. A powerful tool for optimizing such beasts is what is known as an "independent group", @@ -939,10 +957,10 @@ escape it with a backslash. "-" is also taken literally when it is at the end of the list, just before the closing "]". (The following all specify the same class of three characters: C<[-az]>, C<[az-]>, and C<[a\-z]>. All are different from C<[a-z]>, which -specifies a class containing twenty-six characters.) -Also, if you try to use the character classes C<\w>, C<\W>, C<\s>, -C<\S>, C<\d>, or C<\D> as endpoints of a range, that's not a range, -the "-" is understood literally. +specifies a class containing twenty-six characters, even on EBCDIC +based coded character sets.) Also, if you try to use the character +classes C<\w>, C<\W>, C<\s>, C<\S>, C<\d>, or C<\D> as endpoints of +a range, that's not a range, the "-" is understood literally. Note also that the whole range idea is rather unportable between character sets--and even within character sets they may cause results @@ -954,11 +972,11 @@ spell out the character sets in full. Characters may be specified using a metacharacter syntax much like that used in C: "\n" matches a newline, "\t" a tab, "\r" a carriage return, "\f" a form feed, etc. More generally, \I, where I is a string -of octal digits, matches the character whose ASCII value is I. -Similarly, \xI, where I are hexadecimal digits, matches the -character whose ASCII value is I. The expression \cI matches the -ASCII character control-I. Finally, the "." metacharacter matches any -character except "\n" (unless you use C). +of octal digits, matches the character whose coded character set value +is I. Similarly, \xI, where I are hexadecimal digits, +matches the character whose numeric value is I. The expression \cI +matches the character control-I. Finally, the "." metacharacter +matches any character except "\n" (unless you use C). You can specify a series of alternatives for a pattern using "|" to separate them, so that C will match any of "fee", "fie", @@ -1080,7 +1098,7 @@ For example: $_ = 'bar'; s/\w??/<$&>/g; -results in C<"<><><><>">. At each position of the string the best +results in C<< <><><><> >>. At each position of the string the best match given by non-greedy C is the zero-length match, and the I match is what is matched by C<\w>. Thus zero-length matches alternate with one-character-long matches. @@ -1120,7 +1138,7 @@ one match at a given position is possible. This section describes the notion of better/worse for combining operators. In the description below C and C are regular subexpressions. -=over +=over 4 =item C @@ -1262,5 +1280,7 @@ L. L. +L. + I by Jeffrey Friedl, published by O'Reilly and Associates.