fixup: use do...end block to only shell out once

test/helpers.lua

@@ -270,23 +270,29 @@ function module.check_logs()
 end
 
 -- Gets (lowercase) OS name from CMake, uname, or manually check if on Windows
-local function uname()
- local platform
- if os.getenv("SYSTEM_NAME") then -- From CMAKE_HOST_SYSTEM_NAME.
- platform = string.lower(os.getenv("SYSTEM_NAME"))
- return platform
- end
+do
+ local platform = nil
+ function module.uname()
+ if platform then
+  return platform
+  end
 
- local status, f = pcall(module.popen_r, 'uname', '-s')
- if status then
- platform = string.lower(f:read("*l"))
- f:close()
- elseif package.config:sub(1,1) == '\\' then
- platform = 'windows'
- else
- error('unknown platform')
+ if os.getenv("SYSTEM_NAME") then -- From CMAKE_HOST_SYSTEM_NAME.
+ platform = string.lower(os.getenv("SYSTEM_NAME"))
+ return platform
+ end
+
+ local status, f = pcall(module.popen_r, 'uname', '-s')
+ if status then
+ platform = string.lower(f:read("*l"))
+ f:close()
+ elseif package.config:sub(1,1) == '\\' then
+ platform = 'windows'
+ else
+ error('unknown platform')
+ end
+ return platform
  end
- return platform
 end
 
 function module.is_os(s)
@@ -297,11 +303,11 @@ function module.is_os(s)
  or s == 'bsd') then
  error('unknown platform: '..tostring(s))
  end
- return ((s == 'win' and uname() == 'windows')
- or (s == 'mac' and uname() == 'darwin')
- or (s == 'freebsd' and uname() == 'freebsd')
- or (s == 'openbsd' and uname() == 'openbsd')
- or (s == 'bsd' and string.find(uname(), 'bsd')))
+ return ((s == 'win' and module.uname() == 'windows')
+ or (s == 'mac' and module.uname() == 'darwin')
+ or (s == 'freebsd' and module.uname() == 'freebsd')
+ or (s == 'openbsd' and module.uname() == 'openbsd')
+ or (s == 'bsd' and string.find(module.uname(), 'bsd')))
 end
 
 local function tmpdir_get()