From faa7c5eea2de7e053f38c0726c01147531687361 Mon Sep 17 00:00:00 2001
From: Nils Adermann <naderman@naderman.de>
Date: Sun, 19 May 2019 20:52:53 +0200
Subject: [PATCH] Allow overriding self-update target file with envvar
 COMPOSER_SELF_UPDATE_TARGET

Useful if Composer is provided on a read-only filesystems, to allow
self-update to work with a different destination
---
 src/Composer/Command/SelfUpdateCommand.php | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/Composer/Command/SelfUpdateCommand.php b/src/Composer/Command/SelfUpdateCommand.php
index 78b27460e..226aafeb5 100644
--- a/src/Composer/Command/SelfUpdateCommand.php
+++ b/src/Composer/Command/SelfUpdateCommand.php
@@ -351,6 +351,10 @@ TAGSPUBKEY
                 @copy($localFilename, $backupTarget);
             }
 
+            if ($targetFilename = getenv('COMPOSER_SELF_UPDATE_TARGET')) {
+                $localFilename = realpath($targetFilename) ?: $targetFilename;
+            }
+
             rename($newFilename, $localFilename);
 
             return null;