正则表达式中空行和空行的区别

Question

SO 上已经有几个 good discussions of regular expressions and empty lines。如果这个问题重复，我会删除它。

谁能解释为什么这个脚本输出 5 3 4 5 4 3 而不是 4 3 4 4 4 3？当我运行它在调试器中 $blank 和 $classyblank 停留在“4”（我认为这是正确的值）直到打印语句之前。

my ( $blank, $nonblank, $non_nonblank, 
     $classyblank,  $classyspace, $blanketyblank ) = 0 ;

while (<DATA>) {

  $blank++ if /\p{IsBlank}/         ; # POSIXly blank - 4?
  $nonblank++ if /^\P{IsBlank}$/    ; # POSIXly non-blank - 3
  $non_nonblank++ if not /\S/       ; # perlishly not non-blank - 4
  $classyblank++ if /[[:blank:]]/   ; # older(?) charclass blankness - 4?
  $classyspace++ if /^[[:space:]]$/ ; # older(?) charclass whitespace - 4
  $blanketyblank++ if /^$/          ; # perlishly *really empty*  - 3

}

print join " ", $blank, $nonblank, $non_nonblank,
            $classyblank, $classyspace, $blanketyblank , "\n" ;

__DATA__

line above only has a linefeed this one is not blank because: words

this line is followed by a line with white space (you may need to add it)

then another blank line following this one

THE END :-\

这与 __DATA__ 部分有关还是我误解了 POSIX 正则表达式？

ps:

如评论及时postelsewhere,"really empty"(/^$/)可漏非空:

perl -E 'my $string = "\n" . "foo\n\n" ; say "empty" if $string =~ /^$/ ;'
perl -E 'my $string = "\n" . "bar\n\n" ; say "empty" if $string =~ /\A\z/ ;'
perl -E 'my $string = "\n" . "baz\n\n" ; say "empty" if $string =~ /\S/ ;'

Answer 1

/\p{IsBlank}/ 不检查空字符串。 \p 匹配具有指定 Unicode 属性.

的字符

$ unichars '\p{IsBlank}' | cat
 ---- U+0009 CHARACTER TABULATION
 ---- U+0020 SPACE
 ---- U+00A0 NO-BREAK SPACE
 ---- U+1680 OGHAM SPACE MARK
 ---- U+2000 EN QUAD
 ---- U+2001 EM QUAD
 ---- U+2002 EN SPACE
 ---- U+2003 EM SPACE
 ---- U+2004 THREE-PER-EM SPACE
 ---- U+2005 FOUR-PER-EM SPACE
 ---- U+2006 SIX-PER-EM SPACE
 ---- U+2007 FIGURE SPACE
 ---- U+2008 PUNCTUATION SPACE
 ---- U+2009 THIN SPACE
 ---- U+200A HAIR SPACE
 ---- U+202F NARROW NO-BREAK SPACE
 ---- U+205F MEDIUM MATHEMATICAL SPACE
 ---- U+3000 IDEOGRAPHIC SPACE

它匹配 " \n" 因为 SPACE 有 IsBlank 属性.

/[[:blank:]]/ 不检查空字符串。 [...] 匹配属于指定 class.

成员的字符

$ unichars '[[:blank:]]' | cat
 ---- U+0009 CHARACTER TABULATION
 ---- U+0020 SPACE
 ---- U+00A0 NO-BREAK SPACE
 ---- U+1680 OGHAM SPACE MARK
 ---- U+2000 EN QUAD
 ---- U+2001 EM QUAD
 ---- U+2002 EN SPACE
 ---- U+2003 EM SPACE
 ---- U+2004 THREE-PER-EM SPACE
 ---- U+2005 FOUR-PER-EM SPACE
 ---- U+2006 SIX-PER-EM SPACE
 ---- U+2007 FIGURE SPACE
 ---- U+2008 PUNCTUATION SPACE
 ---- U+2009 THIN SPACE
 ---- U+200A HAIR SPACE
 ---- U+202F NARROW NO-BREAK SPACE
 ---- U+205F MEDIUM MATHEMATICAL SPACE
 ---- U+3000 IDEOGRAPHIC SPACE

它匹配 " \n"，因为 SPACE 是 [:blank:] POSIX 字符 class 的成员，因此也是 [[:blank:]] 的成员字符 class.

正则表达式中空行和空行的区别

Differences between empty and blank lines in regexps

regex

perl

posix