“如果”在foreach循环中不存在 - 什么？

Question

当我在if循环中调用foreach comandlet时：

$spisok = Get-Content "OmConv79_2.txt" -TotalCount 100
foreach ($i in $spisok) {
    #Write-Host $i
    $i -match "^(.*)\t(.+)\t?(.*)?" |
        foreach { $Matches[1] + "----" + $Matches[2] + "----" + $Matches[3] } |
        if ($Matches[1] -eq "^\d\d.\d\d.\d\d \d\d:\d\d:\d\d\.\d\d\d\d\d\d") {
            $Matches[0]
        }
}

我收到了这个错误：

if : The term 'if' is not recognized as the name of a cmdlet, function, script file, or
operable program. Check the spelling of the name, or if a path was included, verify that
the path is correct and try again.
At line:7 char:9
+         if ($Matches[1] -eq "^\d\d.\d\d.\d\d \d\d:\d\d:\d\d\.\d\d\d\d ...
+         ~~
    +         CategoryInfo          : ObjectNotFound: (if:String) [], CommandNotFoundException
    +         FullyQualifiedErrorId : CommandNotFoundException

“if”无法识别？我糊涂了。怎么可能？

Answer 1

您无法在管道中直接使用<{1}}语句。

您第二次使用if不是循环，而是在管道中调用ForEach-Object cmdlet 。
遗憾的是，foreach cmdlet别名为ForEach-Object，导致与foreach 关键字（循环结构）混淆。

要在管道中加入foreach语句（有条件），根据您的需要，您有两种选择：

• 如果if语句仅对输入执行过滤 - 有选择地 - 传递，请使用脚本块中的条件if来电（别名：Where-Object，where）

• 如果?语句也生成自定义输出，请将其放在if调用的脚本块中（别名：ForEach-Object，{ {1}}）。

简化示例：

foreach

仅使用%过滤解决方案：

# !! These BREAK - you cannot use `if` directly in a pipeline.
'line 1', 'line 2' | if ($_ -match '1') { $_ }       # filtering only
'line 1', 'line 2' | if ($_ -match '1') { $_ + '!' } # filtering + custom output

使用Where-Object过滤+自定义输出解决方案：

$ 'line 1', 'line 2' | Where-Object { $_ -match '1' }
line 1

至于您的代码：

据我所知（包括后面的评论）， 可以

ForEach-Object

• 请注意使用单个管道，只需一次$ 'line 1', 'line 2' | ForEach-Object { if ($_ -match '1') { $_ + '!' } } line 1! 调用即可处理每个输入行。

• Get-Content "OmConv79_2.txt" -TotalCount 100 | ForEach-Object { # process each line, represented as $_ if ($_ -match '^(.*)\t(.+)\t?(.*)?') { # Is the first tab-separated field a date + time? if ($Matches[1] -match '^\d\d.\d\d.\d\d \d\d:\d\d:\d\d\.\d\d\d\d\d\d') { $Matches[0] # Output the first 3 tab-separated fields. } else { # Output line with default date prepended } } } 必须替换为ForEach-Object以匹配-eq正则表达式。

• 正则表达式是单引号，因此PowerShell的字符串插值不会妨碍。