diff --git a/src/Symfony/Component/Process/Process.php b/src/Symfony/Component/Process/Process.php
index b71d4dadb5f3f..4cb744b7320c7 100644
--- a/src/Symfony/Component/Process/Process.php
+++ b/src/Symfony/Component/Process/Process.php
@@ -288,12 +288,6 @@ public function start(callable $callback = null, array $env = [])
         $this->hasCallback = null !== $callback;
         $descriptors = $this->getDescriptors();
 
-        if ($this->env) {
-            $env += $this->env;
-        }
-
-        $env += $this->getDefaultEnv();
-
         if (\is_array($commandline = $this->commandline)) {
             $commandline = implode(' ', array_map([$this, 'escapeArgument'], $commandline));
 
@@ -301,10 +295,13 @@ public function start(callable $callback = null, array $env = [])
                 // exec is mandatory to deal with sending a signal to the process
                 $commandline = 'exec '.$commandline;
             }
-        } else {
-            $commandline = $this->replacePlaceholders($commandline, $env);
         }
 
+        if ($this->env) {
+            $env += $this->env;
+        }
+        $env += $this->getDefaultEnv();
+
         $options = ['suppress_errors' => true];
 
         if ('\\' === \DIRECTORY_SEPARATOR) {
@@ -1641,17 +1638,6 @@ private function escapeArgument(?string $argument): string
         return '"'.str_replace(['"', '^', '%', '!', "\n"], ['""', '"^^"', '"^%"', '"^!"', '!LF!'], $argument).'"';
     }
 
-    private function replacePlaceholders(string $commandline, array $env)
-    {
-        return preg_replace_callback('/"\$([_a-zA-Z]++[_a-zA-Z0-9]*+)"/', function ($matches) use ($commandline, $env) {
-            if (!isset($env[$matches[1]]) || false === $env[$matches[1]]) {
-                throw new InvalidArgumentException(sprintf('Command line is missing a value for key %s: %s.', $matches[0], $commandline));
-            }
-
-            return '\\' === \DIRECTORY_SEPARATOR ? $this->escapeArgument($env[$matches[1]]) : $matches[0];
-        }, $commandline);
-    }
-
     private function getDefaultEnv(): array
     {
         $env = [];
diff --git a/src/Symfony/Component/Process/Tests/ProcessTest.php b/src/Symfony/Component/Process/Tests/ProcessTest.php
index b29e1ec1e9a69..a596eada035cd 100644
--- a/src/Symfony/Component/Process/Tests/ProcessTest.php
+++ b/src/Symfony/Component/Process/Tests/ProcessTest.php
@@ -1461,46 +1461,6 @@ public function provideEscapeArgument()
         yield [1.1];
     }
 
-    public function testPreparedCommand()
-    {
-        $p = Process::fromShellCommandline('echo "$abc"DEF');
-        $p->run(null, ['abc' => 'ABC']);
-
-        $this->assertSame('ABCDEF', rtrim($p->getOutput()));
-    }
-
-    public function testPreparedCommandMulti()
-    {
-        $p = Process::fromShellCommandline('echo "$abc""$def"');
-        $p->run(null, ['abc' => 'ABC', 'def' => 'DEF']);
-
-        $this->assertSame('ABCDEF', rtrim($p->getOutput()));
-    }
-
-    public function testPreparedCommandWithQuoteInIt()
-    {
-        $p = Process::fromShellCommandline('php -r "$code" "$def"');
-        $p->run(null, ['code' => 'echo $argv[1];', 'def' => '"DEF"']);
-
-        $this->assertSame('"DEF"', rtrim($p->getOutput()));
-    }
-
-    public function testPreparedCommandWithMissingValue()
-    {
-        $this->expectException('Symfony\Component\Process\Exception\InvalidArgumentException');
-        $this->expectExceptionMessage('Command line is missing a value for key "$abc": echo "$abc".');
-        $p = Process::fromShellCommandline('echo "$abc"');
-        $p->run(null, ['bcd' => 'BCD']);
-    }
-
-    public function testPreparedCommandWithNoValues()
-    {
-        $this->expectException('Symfony\Component\Process\Exception\InvalidArgumentException');
-        $this->expectExceptionMessage('Command line is missing a value for key "$abc": echo "$abc".');
-        $p = Process::fromShellCommandline('echo "$abc"');
-        $p->run(null, []);
-    }
-
     public function testEnvArgument()
     {
         $env = ['FOO' => 'Foo', 'BAR' => 'Bar'];