如何在 Perl 正则表达式中替换第 n 次匹配? [英] How can I substitute the nth occurrence of a match in a Perl regex?

问题描述

跟进关于 提取第 n 个正则表达式匹配，如果找到，我现在需要替换匹配.

Following up from an earlier question on extracting the n'th regex match, I now need to substitute the match, if found.

我认为我可以定义提取子例程并使用 /e 修饰符在替换中调用它.我显然错了(诚然，我有一个 XY 问题).

I thought that I could define the extraction subroutine and call it in the substitution with the /e modifier. I was obviously wrong (admittedly, I had an XY problem).

use strict;
use warnings;

sub extract_quoted { # à la codaddict

        my ($string, $index) = @_;
        while($string =~ /'(.*?)'/g) {
                $index--;
                return $1 if(! $index);
        }
        return;
}

my $string = "'How can I','use' 'PERL','to process this' 'line'";

extract_quoted ( $string, 3 );
$string =~ s/&extract_quoted($string,2)/'Perl'/e;

print $string; # Prints 'How can I','use' 'PERL','to process this' 'line'

当然，这种技术还有许多其他问题:

There are, of course, many other issues with this technique:

• 如果在不同位置有相同的匹配怎么办?
• 如果找不到匹配项怎么办?

鉴于这种情况，我想知道可以通过哪些方式实现.

In light of this situation, I'm wondering in what ways this could be implemented.

推荐答案

或者你可以这样做

use strict;
use warnings;

my $string = "'How can I','use' .... 'perl','to process this' 'line'";

my $cont =0;
sub replacen { # auxiliar function: replaces string if incremented counter equals $index
        my ($index,$original,$replacement) = @_;
        $cont++;
        return $cont == $index ? $replacement: $original;
}

#replace the $index n'th match (1-based counting) from $string by $rep
sub replace_quoted {
        my ($string, $index,$replacement) = @_;
        $cont = 0; # initialize match counter
        $string =~ s/'(.*?)'/replacen($index,$1,$replacement)/eg;
        return $string;
}

my $result = replace_quoted ( $string, 3 ,"PERL");
print "RESULT: $result\n";

全局" $cont 变量有点丑，可以改进，但你懂的.

A little ugly the "global" $cont variable, that could be polished, but you get the idea.

更新:更紧凑的版本:

use strict;
my $string = "'How can I','use' .... 'perl','to process this' 'line'";

#replace the $index n'th match (1-based counting) from $string by $replacement
sub replace_quoted {
        my ($string, $index,$replacement) = @_;
        my $cont = 0; # initialize match counter
        $string =~ s/'(.*?)'/$cont++ == $index ? $replacement : $1/eg;
        return $string;
}

my $result = replace_quoted ( $string, 3 ,"PERL");
print "RESULT: $result\n";

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