@@ -2,7 +2,10 @@ module j3s.sh/zoa
 
 go 1.19
 
-require mvdan.cc/sh/v3 v3.5.1
+require (
+	github.com/google/renameio v1.0.1
+	mvdan.cc/sh/v3 v3.5.1
+)
 
 require (
 	golang.org/x/sync v0.1.0 // indirect

@@ -1,6 +1,8 @@ 
 github.com/creack/pty v1.1.17 h1:QeVUsEDNrLBW4tMgZHvxy18sKtr6VI492kBhUfhDJNI=
 github.com/frankban/quicktest v1.14.0 h1:+cqqvzZV87b4adx/5ayVOaYZ2CrvM4ejQvUdBzPPUss=
 github.com/google/go-cmp v0.5.6 h1:BKbKCqvP6I+rmFHt06ZmyQtvB8xAkWdhFyr0ZUNZcxQ=
+github.com/google/renameio v1.0.1 h1:Lh/jXZmvZxb0BBeSY5VKEfidcbcbenKjZFzM/q0fSeU=
+github.com/google/renameio v1.0.1/go.mod h1:t/HQoYBZSsWSNK35C6CO/TpPLDVWvxOHboWUAweKUpk=
 github.com/kr/pretty v0.3.0 h1:WgNl7dwNpEZ6jJ9k1snq4pZsg7DOEN8hP9Xw0Tsjwk0=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/rogpeppe/go-internal v1.8.1 h1:geMPLpDpQOgVyCg5z5GoRwLHepNdb71NXb67XFkP+Eg=

@@ -13,7 +13,6 @@ "mvdan.cc/sh/v3/interp"
 )
 
 func printUsageExit() {
-	// TODO: -v -h
 	fmt.Printf(`usage: zoa <command> [arguments]
 
 commands:
@@ -45,10 +44,16 @@ command := os.Args[1]
 	switch command {
 	case "run":
 		zoaRun()
+	case "fmt":
+		if len(os.Args) <= 2 {
+			fmt.Println("fmt requires 1 argument: the path to a posix shell script")
+			os.Exit(1)
+		}
+		shell.ZoaFmt(os.Args[2])
 	case "cp":
 		var mode os.FileMode
 		if len(os.Args) < 4 {
-			fmt.Println("zoa cp requires at least 2 arguments")
+			fmt.Println("cp requires at least 2 arguments: source and destination")
 			os.Exit(1)
 		}
 		if len(os.Args) == 4 {

@@ -1,6 +1,7 @@ 
 package shell
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"log"
@@ -10,6 +11,7 @@ 
 	"j3s.sh/zoa/color"
 	"j3s.sh/zoa/utils"
 
+	maybeio "github.com/google/renameio/maybe"
 	"mvdan.cc/sh/v3/interp"
 	"mvdan.cc/sh/v3/syntax"
 )
@@ -56,6 +58,35 @@ }
 	defer f.Close()
 	result, err = syntax.NewParser().Parse(f, "")
 	return result, err
+}
+
+func ZoaFmt(script string) {
+	f, err := os.Open(script)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer f.Close()
+
+	p := syntax.NewParser()
+	syntax.KeepComments(true)(p)
+	syntax.Variant(syntax.LangPOSIX)(p)
+	node, err := p.Parse(f, "")
+	if err != nil {
+		return
+	}
+	var writeBuf bytes.Buffer
+	syntax.NewPrinter().Print(&writeBuf, node)
+	res := writeBuf.Bytes()
+
+	info, err := os.Lstat(script)
+	if err != nil {
+		log.Fatal(err)
+	}
+	perm := info.Mode().Perm()
+	// TODO: remove maybeio when golang implements atomic writing
+	if err := maybeio.WriteFile(script, res, perm); err != nil {
+		log.Fatal(err)
+	}
 }
 
 // ZoaCopy copies a file from src to dst, optionally modifying its mode.

@@ -1,7 +1,7 @@ 
 #!/bin/sh
 # test function inheretence
 println() {
-  printf "%s\n" "$1"
+	printf "%s\n" "$1"
 }
 
 # hewo
@@ -9,17 +9,18 @@ uname -a
 PASSTHROUGH=bananas
 
 # test waiting for output, printing a set var
-sleep 2; printf '%s\n' "$PASSTHROUGH"
+sleep 2
+printf '%s\n' "$PASSTHROUGH"
 
 # test if statements
 if [ "$(uname -n)" = "nostromo" ]; then
-  printf "%s\n" NOSTROMO
+	printf "%s\n" NOSTROMO
 fi
-printf "%s\n" "$NODENAME" > /tmp/hi
+printf "%s\n" "$NODENAME" >/tmp/hi
 
 # ensure that suggestions work in an if statement
 if true; then
-    echo hi
+	echo hi
 fi
 
 # test zoa cp