add cataloger selection example (#2646)

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

examples/select_catalogers/main.go

@@ -0,0 +1,78 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"os"
+
+	"github.com/anchore/syft/syft"
+	"github.com/anchore/syft/syft/cataloging/pkgcataloging"
+	"github.com/anchore/syft/syft/sbom"
+	"github.com/anchore/syft/syft/source"
+)
+
+const defaultImage = "alpine:3.19"
+
+func main() {
+	// automagically get a source.Source for arbitrary string input
+	src := getSource(imageReference())
+
+	// catalog the given source and return a SBOM
+	// let's explicitly use catalogers that are:
+	// - for installed software
+	// - used in the directory scan
+	sbom := getSBOM(src, pkgcataloging.InstalledTag, pkgcataloging.DirectoryTag)
+
+	// Show a basic catalogers and input configuration used
+	enc := json.NewEncoder(os.Stdout)
+	enc.SetIndent("", "  ")
+	if err := enc.Encode(sbom.Descriptor.Configuration); err != nil {
+		panic(err)
+	}
+
+}
+
+func imageReference() string {
+	// read an image string reference from the command line or use a default
+	if len(os.Args) > 1 {
+		return os.Args[1]
+	}
+	return defaultImage
+}
+
+func getSource(input string) source.Source {
+	detection, err := source.Detect(input,
+		source.DetectConfig{
+			DefaultImageSource: "docker",
+		},
+	)
+
+	if err != nil {
+		panic(err)
+	}
+
+	src, err := detection.NewSource(source.DefaultDetectionSourceConfig())
+
+	if err != nil {
+		panic(err)
+	}
+
+	return src
+}
+
+func getSBOM(src source.Source, defaultTags ...string) sbom.SBOM {
+	cfg := syft.DefaultCreateSBOMConfig().
+		WithCatalogerSelection(
+			// here you can sub-select, add, remove catalogers from the default selection...
+			// or replace the default selection entirely!
+			pkgcataloging.NewSelectionRequest().
+				WithDefaults(defaultTags...),
+		)
+
+	s, err := syft.CreateSBOM(context.Background(), src, cfg)
+	if err != nil {
+		panic(err)
+	}
+
+	return *s
+}