allow user to override the Usage function

R=gri
DELTA=15  (6 added, 5 deleted, 4 changed)
OCL=31649
CL=31649

diff --git a/src/pkg/flag/flag.go b/src/pkg/flag/flag.go
index 437aaf230a09402e4ab9758fc5dff25a15c93952..af221de9b77e27ceb51026dcace50f7053f3fad6 100644 (file)
--- a/src/pkg/flag/flag.go
+++ b/src/pkg/flag/flag.go
@@ -260,16 +260,11 @@ func PrintDefaults() {
        })
 }
 
-// Usage prints to standard error a default usage message documenting all defined flags and
-// then calls os.Exit(1).
-func Usage() {
-       if len(os.Args) > 0 {
-               fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0]);
-       } else {
-               fmt.Fprintln(os.Stderr, "Usage:");
-       }
+// Usage prints to standard error a default usage message documenting all defined flags.
+// The function is a variable that may be changed to point to a custom function.
+var Usage = func() {
+       fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0]);
        PrintDefaults();
-       os.Exit(1);
 }
 
 func NFlag() int {
@@ -415,6 +410,7 @@ func (f *allFlags) parseOne(index int) (ok bool, next int)
        if len(name) == 0 || name[0] == '-' || name[0] == '=' {
                print("bad flag syntax: ", s, "\n");
                Usage();
+               os.Exit(2);
        }
 
        // it's a flag. does it have an argument?
@@ -432,18 +428,21 @@ func (f *allFlags) parseOne(index int) (ok bool, next int)
        if alreadythere {
                print("flag specified twice: -", name, "\n");
                Usage();
+               os.Exit(2);
        }
        m := flags.formal;
        flag, alreadythere = m[name]; // BUG
        if !alreadythere {
                print("flag provided but not defined: -", name, "\n");
                Usage();
+               os.Exit(2);
        }
        if f, ok := flag.Value.(*boolValue); ok {       // special case: doesn't need an arg
                if has_value {
                        if !f.set(value) {
                                print("invalid boolean value ", value, " for flag: -", name, "\n");
                                Usage();
+                               os.Exit(2);
                        }
                } else {
                        f.set("true")
@@ -459,11 +458,13 @@ func (f *allFlags) parseOne(index int) (ok bool, next int)
                if !has_value {
                        print("flag needs an argument: -", name, "\n");
                        Usage();
+                       os.Exit(2);
                }
                ok = flag.Value.set(value);
                if !ok {
                        print("invalid value ", value, " for flag: -", name, "\n");
                                Usage();
+                               os.Exit(2);
                }
        }
        flags.actual[name] = flag;