Split a string with powershell to get the first and last element

By using String.split() with the count parameter to manage dashes in the commitid:

$x = "0.3.1-15-g3b885c5"
$tag = $x.split("-",3)[0]
$commitid = $x.split("-",3)[-1]

Note: This answer focuses on improving on the split-into-tokens-by-- approach from Richard's helpful answer, though note that that approach isn't fully robust, because git tag names may themselves contain - characters, so you cannot blindly assume that the first - instance ends the tag name.
To account for that, use Richard's robust solution instead.

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Just to offer a more PowerShell-idiomatic variant:

# Stores '0.3.1' in $tag, and 'g3b885c5' in $commitId
$tag, $commitId = ('0.3.1-15-g3b885c5' -split '-')[0, -1]

• PowerShell's -split operator is used to split the input string into an array of tokens by separator -
  While the [string] type's .Split() method would be sufficient here, -split offers many advantages in general.

• [0, -1] extracts the first (0) and last (-1) element from the array returned by -split and returns them as a 2-element array.

• $tag, $commitId = is a destructuring multi-assignment that assigns the elements of the resulting 2-element array to a variable each.

I can't recall if dashes are allowed in tags, so I'll assume they are, but will not appear in the last two fields.

Thus:

if ("0.3.1-15-g3b885c5" -match '(.*)-\d+-([^-]+)') {
  $tag = $Matches[1];
  $commitId = $Matches[2]
}