all: check and return an error if start index is out of range

2 files changed, 5 insertions, 0 deletions

diff --git a/command.go b/command.go
index 0496e5f..aa18c28 100644
--- a/command.go
+++ b/command.go
@@ -83,6 +83,9 @@ func NewCommand(mode, scriptPath string, startAt, endAt int) (cmd *Command, err
 		return nil, fmt.Errorf("%s: %w", logp, err)
 	}
 
+	if cmd.scriptStart >= len(cmd.script.Statements) {
+		return nil, fmt.Errorf("%s: start index out of range", logp)
+	}
 	if cmd.scriptEnd >= len(cmd.script.Statements) {
 		cmd.scriptEnd = len(cmd.script.Statements) - 1
 	}
diff --git a/script.go b/script.go
index 10c09a9..df669bd 100644
--- a/script.go
+++ b/script.go
@@ -68,6 +68,8 @@ func parseScript(env *environment, content []byte) (s *script, err error) {
 	}
 
 	stmts := bytes.Split(buf.Bytes(), []byte{'\n'})
+	// Add empty line at the beginning to make the start index start from
+	// 1, not 0.
 	stmts = append([][]byte{{}}, stmts...)
 
 	s = &script{