Question

SO上已有多个good discussions regular expressions and empty lines。如果它是重复的话，我会删除这个问题。

有人可以解释为什么此脚本会输出5 3 4 5 4 3而不是4 3 4 4 4 3吗？当我在调试器$blank中运行它时，$classyblank保持在“4”（我假设它是正确的值），直到print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 :-\

是否与__DATA__部分有关，还是我误解了POSIX正则表达式？

PS：

正如对elsewhere及时帖子的评论所述，“真空”（/^$/）可能会错过非空虚：

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具有IsBlank属性。

/[[:blank:]]/不检查空字符串。 [...]匹配作为指定类成员的字符。

$ 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字符类的成员，因此是[[:blank:]]字符类的成员。

正则表达式中空行和空行之间的差异

1 个答案: