add parameter expansion, arithmetic, set -e/-x/pipefail, trap, eval, exec

- ${#v}, ${v#p} ${v##p} ${v%p} ${v%%p}, ${v/p/r} ${v//p/r} ${v/#p/r}
  ${v/%p/r}, ${v:off:len}, ${v-w} ${v:=w} ${v:+w} ${v:?msg}; nested ${}
- arithmetic expansion $((...)) with the C operators, ** and assignments
- set -e, set -x, set -o pipefail (also as gosh options, passed on to
  subshells); set shows variables, set -o the options
- trap for EXIT and signals; scripts with an EXIT trap run it on
  SIGINT/SIGTERM/SIGHUP too
- eval, exec (also exec > file without a command), $!, wait pid

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

parser.go

@@ -11,7 +11,6 @@ import (
 	"errors"
 	"fmt"
 	"os"
-	"path"
 	"slices"
 	"strconv"
 	"strings"
@@ -191,8 +190,8 @@ func lexWord(src string, i int) (int, error) {
 			}
 			j = end
 		case ch == '$' && j+1 < len(src) && src[j+1] == '{':
-			if k := strings.IndexByte(src[j:], '}'); k >= 0 {
-				j += k
+			if end := paramEnd(src, j); end >= 0 {
+				j = end
 			}
 		case quote == '"':
 			if ch == '"' {
@@ -990,6 +989,7 @@ func (l *listNode) exec() error {
 			err = entry.andOr.exec()
 		}
 		lastStatus = exitStatus(err)
+		runPendingTraps()
 		if isAbort(err) {
 			return err
 		}
@@ -997,9 +997,18 @@ func (l *listNode) exec() error {
 	return err
 }
 
+// exec runs the and-or list. With set -e, only a failure of the last
+// pipeline ends the shell.
 func (a *andOrNode) exec() error {
+	last := a.first
+	if len(a.rest) > 0 {
+		errexitOff++
+	}
 	err := a.first.exec()
-	for _, part := range a.rest {
+	if len(a.rest) > 0 {
+		errexitOff--
+	}
+	for i, part := range a.rest {
 		lastStatus = exitStatus(err)
 		if isAbort(err) {
 			return err
@@ -1008,11 +1017,29 @@ func (a *andOrNode) exec() error {
 			continue
 		}
 		printError(err)
+		isLast := i == len(a.rest)-1
+		if !isLast {
+			errexitOff++
+		}
 		err = part.pipeline.exec()
+		if !isLast {
+			errexitOff--
+		}
+		last = part.pipeline
+	}
+	if last == a.lastPipeline() {
+		checkErrexit(last, err)
 	}
 	return err
 }
 
+func (a *andOrNode) lastPipeline() *pipelineNode {
+	if len(a.rest) == 0 {
+		return a.first
+	}
+	return a.rest[len(a.rest)-1].pipeline
+}
+
 // runBackground starts the and-or list as a background job. Pipelines run
 // like in the foreground, everything else in a subshell.
 func (a *andOrNode) runBackground() error {
@@ -1030,6 +1057,10 @@ func (a *andOrNode) runBackground() error {
 }
 
 func (pl *pipelineNode) exec() error {
+	if pl.negate {
+		errexitOff++
+		defer func() { errexitOff-- }()
+	}
 	err := pl.cmd.exec()
 	if !pl.negate || isAbort(err) {
 		return err
@@ -1073,7 +1104,9 @@ func (s *simpleNode) run(background bool) error {
 
 func (n *ifNode) exec() error {
 	for i, cond := range n.conds {
+		errexitOff++
 		err := cond.exec()
+		errexitOff--
 		if isAbort(err) {
 			return err
 		}
@@ -1116,7 +1149,9 @@ func (n *whileNode) exec() error {
 
 	var result error
 	for {
+		errexitOff++
 		err := n.cond.exec()
+		errexitOff--
 		if isAbort(err) {
 			return err
 		}
@@ -1290,14 +1325,7 @@ func caseMatch(pattern, word string) (bool, error) {
 	if !isGlob {
 		return word == strings.Join(literal, " "), nil
 	}
-	// path.Match does not let * match a /; NUL can be in neither string
-	toNUL := strings.NewReplacer("/", "\x00")
-	ok, err := path.Match(toNUL.Replace(strings.Join(glob, " ")), toNUL.Replace(word))
-	if err != nil {
-		// An invalid pattern only matches itself
-		return word == strings.Join(literal, " "), nil
-	}
-	return ok, nil
+	return globMatch(strings.Join(glob, " "), word), nil
 }
 
 // expandWordList expands the words of a for loop like the arguments of a