使用PowerShell脚本替换DLL版本信息中的内部版本号

Question

I am new to PowerShell and it seems like a reasonable way to replace the build number in my DLLs (by modifying the .rc files) with the revision number from my SVN repository.

Using PowerShell ISE, I created the following variables:

$1 = "123"
$revision = "230"

Now I am testing my string replacement with the following commands to see how it behaves vs. what I have been reading online. I am expecting to find something that will give me back a file version of 12,3,0,230 :

$pattern = '(^\s*FILEVERSION\s*[0-9]+,[0-9]+,[0-9]+,)[0-9]+$'

' FILEVERSION 12,3,0,0' -replace $pattern, "`$1"
# returns " FILEVERSION 12,3,0,"

' FILEVERSION 12,3,0,0' -replace $pattern, "$1"
# returns "123"

' FILEVERSION 12,3,0,0' -replace $pattern, '$1'
# returns " FILEVERSION 12,3,0,"

' FILEVERSION 12,3,0,0' -replace $pattern, "`$1$revision"
# returns "$1230"

' FILEVERSION 12,3,0,0' -replace $pattern, "`$1`$revision"
# returns " FILEVERSION 12,3,0,$revision"

' FILEVERSION 12,3,0,0' -replace $pattern, "$revision`$1"
# returns "230 FILEVERSION 12,3,0,"

I am surprised by the results from attempts 4 and 6. With attempt 4, why is PowerShell not replacing $revision with "230"? Also with attempt 6, why is it getting replaced properly when it comes before `$1 ? I looked for information about scoping within the replacement string for backticks, and didn't find anything.

Answer 1

In a replacement operation PowerShell first expands the PowerShell variables before handing the match and replacement strings off to the regular expression engine. Hence the replacement string "`$1$revision" is expanded to "$1230" and passed to the regexp engine. Since there is no 1230th captured group to be expanded the backreference remains as-is.

To avoid this issue put the backreference identifier in curly brackets:

'FILEVERSION 12,3,0,0' -replace '...', "`${1}$revision"

That ensures your replacement string consists of the backreference $1 and the string 230 .

---

Notes about what the other approaches are doing (for the sake of completeness):

 ' FILEVERSION 12,3,0,0' -replace '...', "`$1" 

Returns " FILEVERSION 12,3,0," because the entire match is replaced with the backreference to the first capturing group and nothing else.

 ' FILEVERSION 12,3,0,0' -replace '...', "$1" 

Returns "123" because PowerShell expands the variable $1 before it's passed to the regexp engine. The latter just sees the string "123" .

 ' FILEVERSION 12,3,0,0' -replace '...', '$1' 

Same behavior as with the first approach (the single quotes prevent PowerShell from expanding the variable $1 just like escaping the $ does).

 ' FILEVERSION 12,3,0,0' -replace '...', "`$1`$revision" 

Returns " FILEVERSION 12,3,0,$revision" because both $ are escaped, so PowerShell doesn't expand $revision , and for the regexp engine $revision is just an ordinary string.

 ' FILEVERSION 12,3,0,0' -replace '...', "$revision`$1" 

Returns "230 FILEVERSION 12,3,0," because PowerShell expands $revision , but this time the value stands before the backreference, so the regexp engine can expand $1 to the first captured group.