Why can't I echo into a regex-matched output file-CodePudding

I have a file that looks like this:

filename.txt

first line
prefix=C:\Users\me\tmp\out_file.txt
second line
python args

What I'm trying to do is run the python script and then echo the output into the file C:\Users\me\tmp\out_file.txt. Running the script is very easy, but echoing the output is proving difficult. filename.txt is in C:\Users\me\tmp, so I open a powershell terminal there and execute the following:

Get-ChildItem | Get-Content -Raw | Select-String -Pattern "(?smi)(?:prefix=([^\n]*?))$.*?(python .*?)$" | %{echo "hello" > $_.Matches.Groups[1].Value}

What this is doing is matching the python script and the output file (note that in general I will be executing this script for every file, hence the pipes). But this results in the error:

Out-File: The filename, directory name, or volume label syntax is incorrect. : 'C:\Users\me\tmp\out_file.txt'

Now, If I copy and paste that exact filename:

echo "hello" > 'C:\Users\me\tmp\out_file.txt'

The result works perfectly (it also works without the quotes). So my question is, why does this fail in the ForEach-Object loop?

In the end, I will call

ForEach-Object -Parallel {Invoke-Expression $_.Matches.Groups[2].Value > $_.Matches.Groups[1].Value}

Which (hopefully) will pipe the output into the output file, but if there is a better way of achieving this that would be helpful as well.

CodePudding user response：

The issue is that you are capturing the CR (Carriage Return) character at the end of the line. If you look at $_.Matches.Groups[1] you'll see:

Success  : True
Name     : 1
Captures : {1}
Index    : 19
Length   : 29
Value    : C:\Users\me\tmp\out_file.txt

Note the length of 29, but the file path is only 28 characters. If you do:

Get-ChildItem | Get-Content -Raw | Select-String -Pattern "(?smi)(?:prefix=([^\n]*?))$.*?(python .*?)$" | %{$_.Matches.Groups[1].Value.ToCharArray()|%{">$_<"}}

You should see that the last few entries appear as:

>e<
>.<
>t<
>x<
>t<
><

Indicating that there's an invisible character there. You can fix that by altering your regex just a little:

"(?smi)(?:prefix=(.*?))[\r\n] .*?(python .*?)$"