using of NSIS reserved symbol

Hallo,

I could'n find the answer in help.
I use the line:

ExecWait '"net" stop mssql$sqlexpress'

mssql$sqlexpress is the name of service for SQL Server Express and has this symbol ($).
compiler searches for the name sqlexpress,
could'n find it and get the message:
unknown variable/constant "sqlexpress" detected, ignoring (C:\path\installer\NSIS\output.nsi:16)

is there a possibility, to avoid this?

thanks

Use double dollar.

ExecWait '"net" stop mssql$$sqlexpress'

oh,really...
Thank You!