Question

我只是想学习一些Perl，所以我正在通过一个函数来掌握语言。有人可以向我解释一下这个函数到底在做什么吗？

#! /usr/bin/perl 
use strict; 

my %hash; 

&Parse('first.txt'); 
&Parse('second.txt'); 

my $outputpath = 'output.txt'; 
unlink ($outputpath); 
open (OUTPUT, ">>$outputpath") || die "Failed to open OUTPUT ($outputpath) - $!"; 
print OUTPUT "$_ \t" . join("\t", @{$hash{$_}}) . "\n" foreach (sort keys %hash); 
close (OUTPUT) || die "Failed to close OUTPUT ($outputpath) - $!"; 

sub Parse { 
    my $inputpath = shift; 
    open (INPUT, "<$inputpath") || die "Failed to open INPUT ($inputpath) - $!"; 
    while (<INPUT>) { 
        chomp; 
        my @row = split(/\t/, $_); 
        my $col1 = $row[0]; 
        shift @row; 
        push(@{$hash{$col1}}, @row); 
    } 
    close (INPUT) || die "Failed to close INPUT ($inputpath) - $!"; 
    return 1; 
}

我对shift和push以及chomp更感兴趣。

Answer 1

编辑：您发布了一些额外的代码，我也会对此进行评论。

#!/usr/bin/perl 
#The first line (has to be first, hence this comment comes after) allows the linux shell to know 
#this is a perl program, and to call perl to execute it.

#use strict: allow stricter checking of perl syntax. You should always do this.
use strict; 

#declare a global variable called hash - not a very good name...
my %hash; 

#call the method with 'first.txt' as argument
&Parse('first.txt'); 
&Parse('second.txt');  #same thing, different parameter


my $outputpath = 'output.txt'; 

#destroy the file declared above if it exists
unlink ($outputpath); 

# open the file for append (could simple have opened for output and not used the unlink above...)
open (OUTPUT, ">>$outputpath") || die "Failed to open OUTPUT ($outputpath) - $!"; 

#print a line to output 
#the line comes from a foreach loop
#the foreach loop runs over the hash, sorted by key
#each hash entry contains an array, this array is converted by a string using the JOIN function
# the join function will paste the elements of the array into a string, seperated by a tab
print OUTPUT "$_ \t" . join("\t", @{$hash{$_}}) . "\n" foreach (sort keys %hash); 

#Close the outputfile
close (OUTPUT) || die "Failed to close OUTPUT ($outputpath) - $!";

这个程序可能是前段时间写的 - 现代Perl看起来有点不同，并且有一些尚未到达的最佳实践。

不要以此为例说明如何编写Perl。如果你笑得很好，也许Ether会为你改写这个：）

#declare a sub
sub Parse { 
    # the parameters given to a sub are stored in @_. 
    #shift without arguments takes the first element from @_
    my $inputpath = shift; 
    #opens the file "inputpath" into fileglob INPUT. 
    #If this fails, quit with an error message
    open (INPUT, "<$inputpath") || die "Failed to open INPUT ($inputpath) - $!"; 

    #loop over the file one line at the time, putting each line in $_
    while (<INPUT>) { 

        #chop = remove last character. chomp = remove last character if it is a CRLF. 
        #Without arguments, works on $_ 
        chomp; 

        #split the $_ variable (containing the row) 
        #into an array based on the tab character
        my @row = split(/\t/, $_); 

        # take the first element into col1
        my $col1 = $row[0]; 

        # shift it (remove the first element)
        shift @row; 

        # actually both rows above can be just written as one statement:
        my $col1 = shift @row;

        #the $hash variable is probably a global hashref defined somewhere above...
        #the $hash hashref now contains a bucket named with the 'col1' value
        # the value of that bucket is the array of the row we just read
        push(@{$hash{$col1}}, @row); 

        # end the while loop
    } 

    #close the file or die
    close (INPUT) || die "Failed to close INPUT ($inputpath) - $!"; 

    #end the method
    return 1; 
}

Answer 2

查找documentation。

哈希：perldata
shift
chomp

Answer 3

如果你有一个健全的perl安装，以下命令行命令将有所帮助：

perldoc -f shift
perldoc -f push
perldoc -f chomp

你也会喜欢：

perldoc perlfunc
perldoc perlvar

不要错过关于perlvar的{{1}}部分，否则你将无法获得perl的内容。

你会逐渐注意到perl不是面向对象的，它支持对象，但这是一个非常奇怪的实现。 Perl更多完成工作，工作通常与某种数据集的提取或翻译有关。

Perl one liners是你将要编写的最强大的命令行：

$_

查看perl -pe 's/(\d*)/$1*10/ge'

中的-p，-e，-n和-i开关

（这是Perl 6被安排作为重大改写的主要原因之一，现在只有在始终并且计划在 Duke Nukem Forever ）

无论如何，{p> perldoc perlrun就像是python的shift或javascript的some_array.pop(1)等。

some_array.shift()就像python的push或javascript的some_array.append(junk)等。

some_array.push(more_junk)非常奇特，实际上是chomp的跨平台版本：它从已从stdin读取的行中删除行尾字符。克服这个小钻石操作员＆lt;＆gt;这是一种破解。（检查chop - “I / O操作符”部分）缺陷：diamond逐行读取stdin或命令行文件参数，但它不会删除perldoc perlop。（也不是\n）
之后
\r\n删除它们。（chomp仅移除chop并单独留下\n。）

这个Perl函数有什么作用？

3 个答案: