Add a few useful os calls to nimscript (#7442)

tests/newconfig/tfoo.nims

@@ -30,4 +30,51 @@ putEnv("dummy", "myval")
 doAssert(existsEnv("dummy") == true)
 doAssert(getEnv("dummy") == "myval")
 
+# issue #7393
+let wd = getCurrentDir()
+cd("..")
+assert wd != getCurrentDir()
+cd(wd)
+assert wd == getCurrentDir()
 
+assert findExe("nim") != ""
+
+# general tests
+mode = ScriptMode.Verbose
+
+assert getCommand() == "c"
+setCommand("cpp")
+assert getCommand() == "cpp"
+setCommand("c")
+
+assert cmpic("HeLLO", "hello") == 0
+
+assert fileExists("tests/newconfig/tfoo.nims") == true
+assert dirExists("tests") == true
+
+assert existsFile("tests/newconfig/tfoo.nims") == true
+assert existsDir("tests") == true
+
+discard selfExe()
+
+when defined(windows):
+  assert toExe("nim") == "nim.exe"
+  assert toDll("nim") == "nim.dll"
+else:
+  assert toExe("nim") == "nim"
+  assert toDll("nim") == "libnim.so"
+
+rmDir("tempXYZ")
+assert dirExists("tempXYZ") == false
+mkDir("tempXYZ")
+assert dirExists("tempXYZ") == true
+assert fileExists("tempXYZ/koch.nim") == false
+cpFile("koch.nim", "tempXYZ/koch.nim")
+assert fileExists("tempXYZ/koch.nim") == true
+cpDir("nimsuggest", "tempXYZ/.")
+assert dirExists("tempXYZ/tests") == true
+assert fileExists("tempXYZ/nimsuggest.nim") == true
+rmFile("tempXYZ/koch.nim")
+assert fileExists("tempXYZ/koch.nim") == false
+rmDir("tempXYZ")
+assert dirExists("tempXYZ") == false