在 perl 中，替换文本中的反向引用后跟数字文字 [英] In perl, backreference in replacement text followed by numerical literal

问题描述

我在替换文本中后跟文字时遇到反向引用问题.我尝试了以下方法:

I'm having trouble with a backreference in my replacement text that is followed by a literal. I have tried the following:

perl -0pi -e "s/(<tag1>foo<\/tag1>\n\s*<tag2>)[^\n]*(<\/tag2>)/\1${varWithLeadingNumber}\2/" file.xml
perl -0pi -e "s/(<tag1>foo<\/tag1>\n\s*<tag2>)[^\n]*(<\/tag2>)/\g{1}${varWithLeadingNumber}\g{2}/" file.xml

第一个当然会导致问题，因为 ${varWithLeadingNumber} 以数字开头，但我认为上面第二次尝试中的 \g{1} 构造应该可以解决这个问题.我使用的是 perl 5.12.4.

The first of course causes problems because ${varWithLeadingNumber} begins with a number, but I thought the \g{1} construct in my second attempt above was supposed to solve this problem. I'm using perl 5.12.4.

推荐答案

在替换表达式中使用\1、\2等是错误的.\1 是一个正则表达式模式，表示匹配第一个捕获匹配的内容"，这在替换表达式中没有意义.不应在正则表达式之外使用正则表达式模式！$1、$2 等是你应该在那里使用的.

Using \1, \2, etc in the replacement expression is wrong. \1 is a regular expression pattern that means "match what the first capture matched" which makes no sense in a replacement expression. Regular expression patterns should not be used outside of regular expressions! $1, $2, etc is what you should be using there.

修复\1后，你有

perl ... -e'... s/.../...$1$varWithLeadingNumber.../ ...'

也就是说，我认为 varWithLeadingNumber 应该是一个 shell 变量?如果它是 Perl 变量，您应该不会有任何问题.如果您让 shell 对 varWithLeadingNumber 进行插值，则可以使用

That said, I think varWithLeadingNumber is supposed to be a shell variable? You shouldn't have any problems if it's a Perl variable. If you're having the shell interpolate varWithLeadingNumber, the problem can be fixed using

perl ... -e"... s/.../...\${1}${varWithLeadingNumber}.../ ..."

请注意，如果 $varWithLeadingNumber 包含$"、@"、\"或/"，则会出现问题，因此您可能需要使用命令行参数而不是插值.

Note that you will have problems if $varWithLeadingNumber contains "$", "@", "\" or "/", so you might want to use a command line argument instead of interpolation.

perl ... -pe'
   BEGIN { $val = shift; }
   ... s/.../...$1$val.../ ...
' "${varWithLeadingNumber}"

您也可以使用环境变量.

You could also use an environment variable.

export varWithLeadingNumber
perl ... -pe's/.../...$1$ENV{varWithLeadingNumber}.../'

或

varWithLeadingNumber=varWithLeadingNumber \
    perl ... -pe's/.../...$1$ENV{varWithLeadingNumber}.../'

<小时>

如果你有 \1

s/...\1.../.../

您可以通过多种方式避免该问题，包括

you can avoid the problem a number of ways including

s/...(?:\1).../.../

这篇关于在 perl 中，替换文本中的反向引用后跟数字文字的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！