From 83c52e3e7023b69cdd5d89d50aa97859149edc6a Mon Sep 17 00:00:00 2001
From: bth <git@bth.moi>
Date: Wed, 21 Jan 2026 12:43:12 -0800
Subject: [PATCH] cat : first naive version

---
 cat/cat.go | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 cmd/cmd.go |  1 +
 um.go      |  3 +++
 3 files changed, 62 insertions(+)
 create mode 100644 cat/cat.go

diff --git a/cat/cat.go b/cat/cat.go
new file mode 100644
index 0000000..04c4e5f
--- /dev/null
+++ b/cat/cat.go
@@ -0,0 +1,58 @@
+package cat
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+
+	"github.com/brtholomy/um/go/cmd"
+	"github.com/brtholomy/um/go/flags"
+	"github.com/brtholomy/um/go/pipe"
+)
+
+const (
+	CMD       = cmd.Cat
+	SUMMARY   = "cat um files together using a filelist"
+	SEPARATOR = "\n---\n\n"
+)
+
+type options struct {
+	Filelist flags.Arg
+	Help     flags.Flag[bool]
+}
+
+func initOpts() options {
+	return options{
+		flags.Arg{"", "filelist. accepts from stdin if not provided"},
+		flags.Flag[bool]{"--help", "-h", false, "show help"},
+	}
+}
+
+func cat(files []string) (string, error) {
+	// strings.Builder ?
+	// can we estimate needed size? do an ls -S call?
+	ff := []string{}
+	for _, f := range files {
+		dat, err := os.ReadFile(f)
+		if err != nil {
+			return "", fmt.Errorf("error opening file: %w", err)
+		}
+		ff = append(ff, string(dat))
+	}
+	return strings.Join(ff, SEPARATOR), nil
+}
+
+func Cat(args []string) {
+	opts := initOpts()
+	flags.ParseArgs(CMD, SUMMARY, args, &opts)
+	files, err := pipe.FileListSplitMaybeStdin(opts.Filelist.Val)
+	if err != nil {
+		log.Fatalf("um %s: %s", CMD, err)
+	}
+	s, err := cat(files)
+	if err != nil {
+		log.Fatalf("um %s: %s", CMD, err)
+	}
+	fmt.Println(s)
+}
diff --git a/cmd/cmd.go b/cmd/cmd.go
index f38ae64..5f2345d 100644
--- a/cmd/cmd.go
+++ b/cmd/cmd.go
@@ -7,5 +7,6 @@ const (
 	Next Subcommand = "next"
 	Last Subcommand = "last"
 	Sort Subcommand = "sort"
+	Cat  Subcommand = "cat"
 	Help Subcommand = "help"
 )
diff --git a/um.go b/um.go
index 6f57d20..97d9782 100644
--- a/um.go
+++ b/um.go
@@ -5,6 +5,7 @@ import (
 	"log"
 	"os"
 
+	"github.com/brtholomy/um/go/cat"
 	"github.com/brtholomy/um/go/cmd"
 	"github.com/brtholomy/um/go/last"
 	"github.com/brtholomy/um/go/next"
@@ -44,6 +45,8 @@ func main() {
 		tag.Tag(args)
 	case cmd.Sort:
 		sort.Sort(args)
+	case cmd.Cat:
+		cat.Cat(args)
 	case cmd.Help:
 		log.Fatalln(helpLong)
 	default: