From 7d779cb6f24aa37e36fe48ec9429242df5a2f0d0 Mon Sep 17 00:00:00 2001
From: Matthew Lesko <matthew.w.lesko@nasa.gov>
Date: Wed, 6 May 2026 13:34:41 -0400
Subject: [PATCH] add flag/envvar to choose temp directory

the `sync` command uses `"github.com/lanrat/extsort"` to create a
temporary directory (and files) for computing what to copy

this PR adds a command line flag (& equivalent environment variable) to
control where the directory is created. without it set, you always get
the "intelligent choice", such as `/tmp`, but users have plenty of
reasons to choose a different directory (`/tmp` too small, faster
location that `extsort` didn't notice, etc.)

Ref: https://github.com/lanrat/extsort#temporary-directory-selection

example usage:

```
s5cmd sync --sort-temp-dir=/scratch FILE s3://[somewhere]/FILE
```

or

```
export S5CMD_SORT_TEMP_DIR=/scratch
s5cmd sync FILE s3://[somewhere]/FILE
```
---
 command/sync.go | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/command/sync.go b/command/sync.go
index 6dede5a66..3c60434ab 100644
--- a/command/sync.go
+++ b/command/sync.go
@@ -85,6 +85,11 @@ func NewSyncCommandFlags() []cli.Flag {
 			Name:  "exit-on-error",
 			Usage: "stops the sync process if an error is received",
 		},
+		&cli.StringFlag{
+			Name:    "sort-temp-dir",
+			Usage:   "directory for temporary files used when sorting objects to compute the source/destination diff (defaults to the OS temp dir)",
+			EnvVars: []string{"S5CMD_SORT_TEMP_DIR"},
+		},
 	}
 	sharedFlags := NewSharedFlags()
 	return append(syncFlags, sharedFlags...)
@@ -131,6 +136,7 @@ type Sync struct {
 	delete      bool
 	sizeOnly    bool
 	exitOnError bool
+	sortTempDir string
 
 	// s3 options
 	storageOpts storage.Options
@@ -155,6 +161,7 @@ func NewSync(c *cli.Context) Sync {
 		delete:      c.Bool("delete"),
 		sizeOnly:    c.Bool("size-only"),
 		exitOnError: c.Bool("exit-on-error"),
+		sortTempDir: c.String("sort-temp-dir"),
 
 		// flags
 		followSymlinks: !c.Bool("no-follow-symlinks"),
@@ -335,6 +342,7 @@ func (s Sync) getSourceAndDestinationObjects(ctx context.Context, cancel context
 		NumWorkers:         extsortDefaultConfig.NumWorkers,
 		ChanBuffSize:       extsortChannelBufferSize,
 		SortedChanBuffSize: extsortChannelBufferSize,
+		TempFilesDir:       s.sortTempDir,
 	}
 	extsortDefaultConfig = nil