Skip to content
fuck-powershell

Double-quoted regex interpolates $vars — and backslash won't save you

args quoting · case

bothmisleading-errorscriptcifirst-partyrepro: verifiedstring-interpolation
Affectspowershell 51, pwsh 7, windows
Fails asUNSET VARIABLE
Mechanismstring interpolation
Safe fixsingle quote regex

Symptom

Section titled “Symptom”

A test asserts against a regex like "SetEnvironmentVariable\(\$entries..." in a double-quoted string. Under Set-StrictMode it explodes with “variable ‘$entries’ cannot be retrieved” — or worse, without StrictMode it silently matches garbage because $entries expanded to nothing.

Repro

Section titled “Repro”
Terminal window
Set-StrictMode -Version Latest
$text -match "pattern(\$entries -join)"
# ERROR: The variable '$entries' cannot be retrieved because it has not been set.
# The backslash did NOT escape the dollar — \ is not an escape char in PowerShell.

Cause

Section titled “Cause”

Two habits from other languages collide: PowerShell interpolates $var inside DOUBLE-quoted strings, and its escape character is the backtick — backslash has no escaping power. A regex written for .NET/PCRE with \$ still interpolates. The variable expands at string-construction time, before the regex engine sees anything.

Workaround

Section titled “Workaround”
  • Write regexes that mention $ in SINGLE quotes: 'pattern(\$entries)' — no interpolation, backslash reaches the regex engine intact.
  • If double quotes are unavoidable, escape with backtick: "\$entries”`.

Refs

Section titled “Refs”