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Joining command fragments with '; ' splits Start-Process mid-call

args quoting · case

bothsilentscriptagentfirst-partyrepro: verifiedstatement-terminator
Affectsnode, powershell 51, pwsh 7, windows
Fails assilent
Mechanismstatement terminator
Safe fixspace join params

Symptom

Section titled “Symptom”

An elevation launcher builds one Start-Process invocation from string fragments and joins them with "; ". The elevated process starts — but without its arguments and without the UAC verb, so the elevated action silently does the wrong thing (or nothing).

Repro

Section titled “Repro”
// Generator code building a PowerShell command line:
const cmd = ["Start-Process -FilePath 'app.exe'", "-ArgumentList 'install'", "-Verb RunAs"].join("; ");
// Produces: Start-Process -FilePath 'app.exe'; -ArgumentList 'install'; -Verb RunAs
// → Start-Process runs with NO args; the rest are separate (broken) statements.

Cause

Section titled “Cause”

; is PowerShell’s statement terminator. A generator that joins PARAMETER fragments of one call with "; " inserts statement boundaries mid-command. Each fragment after the first is parsed as a new statement starting with a parameter token — a parse error at best, a silently degraded Start-Process at worst.

Workaround

Section titled “Workaround”
  • Join parameter tokens of a single call with spaces (or build an array and splat); place ; only BETWEEN complete statements.
  • The fix joined fragments with “” and kept ; only after the complete Start-Process ... -Wait.

Refs

Section titled “Refs”