How to replace last part of a string dynamically?

Question

i have the following

$file_input = "cube1_server1_partial.xml"
$CUBEName = [io.path]::GetFileNameWithoutExtension($file_input).ToUpper() -replace "_partial" #strips extension from $file_input

this results in: cube1_server1

now i have other file names that came into light, such as

cube1_server1_full.xml

i want a comprehensive replacement that doesnt necessarily have to hard code the suffix, so instead of -replace "_partial"

it should be something like -replace "_*" from the end of a string

how can i have a comprehensive replace? maybe with regex?

So you want it to always remove the last `_` and everything following it? — Mathias R. Jessen, Aug 13 '19 at 20:46
`$file_input -replace "_[^_]*$"` will probably work for most cases. — AdminOfThings, Aug 13 '19 at 20:50

score 3 · Answer 1 · answered Aug 13 '19 at 21:06

3

this is yet another method to get the cleaned file name. [grin] however, if you have many such items to clean up, then the regex posted by Mathias R. Jessen is likely your best bet for speed.

what it does ...

split the string on the dot & save the parts into $Name & $Extension
split the $Name on _, skip the last item, rejoin the parts with _
join $WantedNamePart & $Extension with a .
display the results

the code ...

$FileName = 'cube1_server1_partial.xml'

$Name, $Extension = $FileName.Split('.')
$WantedNamePart = ($Name.Split('_') |
    Select-Object -SkipLast 1) -join '_'

$CleanedFileName = $WantedNamePart, $Extension -join '.'

$CleanedFileName

output ...

cube1_server1.xml

answered Aug 13 '19 at 21:06

Lee_Dailey

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interesting, i didnt know you can do this: $Name, $Extension = – Cataster Aug 13 '19 at 21:07
3

Multi-value assignments are fun, you can even swap two variable values in one statement `$Name,$Extension = $Extension,$Name` :D – Mathias R. Jessen Aug 13 '19 at 21:10
1

@Cataster - yep, the multiple assignment thing is occasionally quite handy. [*grin*] – Lee_Dailey Aug 13 '19 at 21:33
@MathiasR.Jessen thats like replacing a variable with temp, sweet! – Cataster Aug 13 '19 at 21:34

score 3 · Answer 2 · answered Aug 14 '19 at 03:02

Yet another solution:

PS> 'cube1_server1_partial.xml' -replace '(.*)_.*', '$1'
cube1_server1

(.*)_ greedily matches through the last _ and captures everything before it (.*) in the 1st capture group ((...)).
.* matches the rest, which ensures that the overall regex matches the entire input string.
Replacement string $1 then replaces the entire string with what the 1st capture group captured, which is everything before the last _.

See this answer for more information about the -replace operator.

Mathias R. Jessen · Accepted Answer · 2019-08-13T20:57:44.667

If you want to remove the last _ and everything following it from a string, you have a couple of options.

Use String.LastIndexOf() and String.Remove():

$string = 'cube1_server1_partial'
$last_index = $string.LastIndexOf('_')
if($last_index -ne -1){
    $string = $string.Remove($last_index)
}

Or you could use the -replace regex operator with a more descriptive pattern:

$string = 'cube1_server1_partial'
$string -replace '(?<=.+)_[^_]*$'

The regex in the example above consists of:

(?<=  # positive look-behind assertion
  .+  # for 1 or more characters
)
_     # a literal underscore
[^_]* # any character that's NOT an underscore, 0 or more times
$     # followed by end of string

The look-behind ensure you don't end up with an empty string if the only _ occurs at position 0, eg. _partial would just return as is. For the non-regex method the equivalent would be to check for $last_index -gt 0 instead of -ne -1

How to replace last part of a string dynamically?

3 Answers3