正则表达式 – 如何在Perl中检测空行？

问题不在于如何找到空白行.问题不在于使用哪个正则表达式.根本问题是理解如何分析问题并将分析转化为代码.

在这种情况下,问题是“我如何解析这种格式？”

我已经为你写了一个解析器.我还花时间写了我用来写它的过程的详细描述.

警告：解析器未针对所有情况进行仔细测试.它没有足够的内置错误处理.对于这些功能,您可以请求价目表或自己编写.

这是您提供的数据样本(我不确定您从中提取了哪些问题)：

constant fixup GemEstabCommDelay = <U2 20>
    vid = 6
    name = "ESTABLISHCOMMUNICATIONSTIMEOUT"
    units = "s"
    min = <U2 0>
    max = <U2 1800>
    default = <U2 20>


constant fixup private GemConstantFileName = <A "C:TMPCONST.LOG">
    vid = 4
    name = ""  units = ""


constant fixup private GemAlarmFileName = <A "C:TMPALARM.LOG">
    vid = 0
    name = ""
    units = ""

在为数据文件编写解析器之前,需要先描述文件的结构.如果您使用的是标准格式(比如XML),则可以阅读现有规范.如果您使用的是本土格式,您可以自己编写.

因此,根据示例数据,我们可以看到：

>数据被分成块.
>每个块以第0列中的单词常量开头.
>每个块以空行结束.
>块由起始行和零个或多个附加行组成.
>起始行由关键字常量后跟一个或多个以空格分隔的单词,’=’符号和<>组成.引用数据值.

>最后一个关键字似乎是常量的名称.称之为constant_name
><> – 引用数据似乎是组合的类型/值说明符.
>早期的关键字似乎指定了有关常量的其他元数据.我们称之为选项.

>附加行指定其他键值对.我们称之为属性.属性可以具有单个值,也可以具有类型/值说明符.
>一个或多个属性可能出现在一行中.

好的,现在我们有一个粗略的规范.我们用它做什么？

格式是如何构建的？考虑从最大到最小的组织逻辑单位.这些将决定我们的代码的结构和流程.

>文件由BLOCKS组成.
> BLOCKS由LINES制成.

所以我们的解析器应该将文件分解为块,然后处理块.

现在我们在评论中粗略化了一个解析器：

# Parse a constant spec file.

# Until file is done:
    # Read in a whole block
    # Parse the block and return key/value pairs for a hash.

    # Store a ref to the hash in a big hash of all blocks,keyed by constant_name.

# Return ref to big hash with all block data

现在我们开始填写一些代码：

# Parse a constant spec file.
sub parse_constant_spec {
    my $fh = shift;

    my %spec;

    # Until file is done:
        # Read in a whole block
    while( my $block = read_block($fh) ) {

        # Parse the and return key/value pairs for a hash.
        my %constant = parse_block( $block );

        # Store a ref to the hash in a big hash of all blocks,keyed by constant_name.
        $spec{ $constant{name} } = %constant;

    }

    # Return ref to big hash with all block data
    return %spec;
}

但它不会起作用.尚未编写parse_block和read_block subs.在这个阶段,没关系.关键在于以小的,可理解的块为特征的粗糙.每隔一段时间,为了保持可读性,你需要掩盖子程序中的细节下降 – 否则你最终会遇到无法调试的可怕的1000行潜艇.

现在我们知道我们需要编写几个子程序来完成,et viola：

#!/usr/bin/perl
use strict;
use warnings;

use Data::Dumper;

my $fh = *DATA;

print Dumper parse_constant_spec( $fh );


# Parse a constant spec file.
# Pass in a handle to process.
# As long as it acts like a file handle,it will work.
sub parse_constant_spec {
    my $fh = shift;

    my %spec;

    # Until file is done:
        # Read in a whole block
    while( my $block = read_block($fh) ) {

        # Parse the and return key/value pairs for a hash.
        my %constant = parse_block( $block );

        # Store a ref to the hash in a big hash of all blocks,keyed by constant_name.
        $spec{ $constant{const_name} } = %constant;

    }

    # Return ref to big hash with all block data
    return %spec;
}

# Read a constant definition block from a file handle.
# void return when there is no data left in the file.
# Otherwise return an array ref containing lines to in the block. 
sub read_block {
    my $fh = shift;

    my @lines;
    my $block_started = 0;

    while( my $line = <$fh> ) {

        $block_started++ if $line =~ /^constant/;

        if( $block_started ) {

            last if $line =~ /^s*$/;

            push @lines,$line;
        }
    }

    return @lines if @lines;

    return;
}


sub parse_block {
    my $block = shift;
    my ($start_line,@attribs) = @$block;

    my %constant;

    # Break down first line:
    # First separate assignment from option list.
    my ($start_head,$start_tail) = split /=/,$start_line;

    # work on option list
    my @options = split /s+/,$start_head;

    # Recover constant_name from options:
    $constant{const_name} = pop @options;
    $constant{options} = @options;

    # Now we parse the value/type specifier
    @constant{'type','value' } = parse_type_value_specifier( $start_tail );

    # Parse attribute lines.
    # since we've already got multiple per line,get them all at once.
    chomp @attribs;
    my $attribs = join ' ',@attribs;

    #  we have one long line of mixed key = "value" or key = <TYPE VALUE> 

    @attribs = $attribs =~ /s*(w+s+=s+".*?"|w+s+=s+<.*?>)s*/g;

    for my $attrib ( @attribs ) {
        warn "$attribn";
        my ($name,$value) = split /s*=s*/,$attrib;

        if( $value =~ /^"/ ) { 
            $value =~ s/^"|"s*$//g;
        }
        elsif( $value =~ /^</ ) {
           $value = [ parse_type_value_specifier( $start_tail ) ];
        }
        else {
            warn "Bad line";
        }

        $constant{ $name } = $value;
    }

    return %constant;
}

sub parse_type_value_specifier {
    my $tvs = shift;

    my ($type,$value) = $tvs =~ /<(w+)s+(.*?)>/;

    return $type,$value;
}

__DATA__
constant fixup GemEstabCommDelay = <U2 20>
    vid = 6
    name = "ESTABLISHCOMMUNICATIONSTIMEOUT"
    units = "s"
    min = <U2 0>
    max = <U2 1800>
    default = <U2 20>


constant fixup private GemConstantFileName = <A "C:TMPCONST.LOG">
    vid = 4
    name = ""  units = ""


constant fixup private GemAlarmFileName = <A "C:TMPALARM.LOG">
    vid = 0
    name = ""
    units = ""

上面的代码远非完美. IMO,parse_block太长了,应该分成更小的子.此外,对形式良好的输入的验证和执行还不够.变量名称和描述可能更清楚,但我并不真正理解数据格式的语义.更好的名称将更接近地匹配数据格式的语义.

尽管存在这些问题,但它确实解析了您的格式并生成了一个非常方便的数据结构,可以填充到您想要的任何输出格式中.

如果您在许多地方使用此格式,我建议将解析代码放入模块中.有关详细信息,请参阅perldoc perlmod.

现在,请停止使用全局变量并忽略好的建议.请开始阅读perldoc,阅读Learning Perl和Perl Best Practices,使用strict,使用警告.当我在阅读阅读列表时,请阅读Global Variables are Bad,然后在wiki周围漫步阅读和学习.通过阅读c2,我学到了更多关于编写软件的知识.

如果您对此代码的工作方式有疑问,为什么要按原样布局,可以做出其他选择,说出来并提出问题.我愿意帮助一个自愿的学生.

你的英语很好,但很明显你不是母语.我可能使用了太多复杂的句子.如果你需要用简单的句子写的部分,我可以尝试帮助.我知道用外语工作非常困难.