如何在Powershell脚本中替换特定关键字后的文件中的N个字符?

Question

我有一个文件原型如下:

// <some stuff>
#define KEYWORD release01-11
// <more stuff>

如何删除与KEYWORD同一行中的最后两个字符并用两个不同的字符(在本例中为12)替换它们，以结束:

// <some stuff>
#define KEYWORD release01-12
// <more stuff>

我试图使用Clear-Content和Add-Content，但我不能让它做我需要的。替换这些符号后，文件的其余部分需要保持不变。有没有更好的选择?

Answer 1

使用-replaceregex运算符识别相关语句并替换/删除尾随的数字:

# read file into a variable
$code = Get-Content myfile.c
# replace the trailing -XX with 12 in all lines starting with `#define KEYWORD`, with 
$code = $code -replace '(?<=#define KEYWORD .+-)d{2}s*$','12'
# write the contents back to the file
$code |Set-Content myfile.c

正则表达式结构(?<=...)是一个积极的向后看-它确保以下表达式只匹配它后面的文本是#define KEYWORD，后面跟着一些字符和-的位置。

---

如果你想总是增加当前值(而不是仅仅用12替换它)，我们需要一些方法来检查和评估当前值在做替换之前。

[Regex]::Replace()方法只允许:

# read file into a variable
$code = Get-Content myfile.c
$code = $code |ForEach-Object {
# Same as before, but now we can hook into the regex engine's substitution routine
[regex]::Replace($_, '(?<=#define KEYWORD .+-)d{2}s*$',{
param($m)
# extract the trailing numbers, convert to a numerical type
$value = $m.Value -as [int]
# increment the value
$value++
# return the new value
return $value
})
}
# write the contents back to the file
$code |Set-Content myfile.c

在PowerShell 6.1及更高版本中，-replace操作符原生支持scriptblock替换:

$code = $code |ForEach-Object {
# Same as before, but now we can hook into the regex engine's substitution routine
$_ -replace '(?<=#define KEYWORD .+-)d{2}s*$',{
# extract the trailing numbers, convert to a numerical type
$value = $_.Value -as [int]
# increment the value
$value++
# return the new value
return $value
}
}