script: Implement regexp filtering for help

Filter the commands shown by 'help' with a regexp instead
of searching by name. This will become useful when there are
many commands sharing the same prefix, for example StateDB has
11 commands and with this we can dump the help for all of them with
'help ^db'.

Signed-off-by: Jussi Maki <[email protected]>

script/cmds.go

@@ -716,11 +716,13 @@ func Help() Cmd {
 	return Command(
 		CmdUsage{
 			Summary: "log help text for commands and conditions",
-			Args:    "[-v] name...",
+			Args:    "[-v] (regexp)",
 			Detail: []string{
 				"To display help for a specific condition, enclose it in brackets: 'help [amd64]'.",
 				"To display complete documentation when listing all commands, pass the -v flag.",
+				"Commands can be filtered with a regexp: 'help ^db'",
 			},
+			RegexpArgs: firstNonFlag,
 		},
 		func(s *State, args ...string) (WaitFunc, error) {
 			if s.engine == nil {
@@ -757,7 +759,7 @@ func Help() Cmd {
 				if len(args) == 0 {
 					out.WriteString("\ncommands:\n\n")
 				}
-				s.engine.ListCmds(out, verbose, cmds...)
+				s.engine.ListCmds(out, verbose, strings.Join(cmds, " "))
 			}
 
 			wait := func(*State) (stdout, stderr string, err error) {

script/engine.go

@@ -58,6 +58,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"regexp"
 	"sort"
 	"strings"
 	"time"
@@ -752,25 +753,26 @@ func checkStatus(cmd *command, err error) error {
 // ListCmds prints to w a list of the named commands,
 // annotating each with its arguments and a short usage summary.
 // If verbose is true, ListCmds prints full details for each command.
-//
-// Each of the name arguments should be a command name.
-// If no names are passed as arguments, ListCmds lists all the
-// commands registered in e.
-func (e *Engine) ListCmds(w io.Writer, verbose bool, names ...string) error {
-	if names == nil {
-		names = make([]string, 0, len(e.Cmds))
-		for name := range e.Cmds {
-			names = append(names, name)
+func (e *Engine) ListCmds(w io.Writer, verbose bool, regexMatch string) error {
+	var re *regexp.Regexp
+	if regexMatch != "" {
+		var err error
+		re, err = regexp.Compile(regexMatch)
+		if err != nil {
+			return err
 		}
-		sort.Strings(names)
 	}
+	names := make([]string, 0, len(e.Cmds))
+	for name := range e.Cmds {
+		names = append(names, name)
+	}
+	sort.Strings(names)
 
 	for _, name := range names {
-		cmd, ok := e.Cmds[name]
-		if !ok {
-			fmt.Fprintf(w, "command %q not found\n", name)
+		if re != nil && !re.MatchString(name) {
 			continue
 		}
+		cmd := e.Cmds[name]
 		usage := cmd.Usage()
 
 		suffix := ""

script/scripttest/testdata/basic.txt

@@ -21,8 +21,14 @@ wait
 # Test help in various ways
 help
 help wait
+grep wait
 help -v wait
+grep wait
 help unknowncommand
+help ^e
+! grep wait
+grep ^exec
+grep ^exists
 
 -- hello.txt --
 hello world