I'm using php to invoke gpg, but I'm getting a pipe error. I thought that if I read in the password from a file, I could then pipe it to the command itself? But, I keep getting: Syntax error: "|" unexpected

Here's the code:

(Note: The files are being iterated over in a foreach loop...)

foreach($files as $k => $v) {
    $encrypted = $v;
    $filename = explode('.',$v);
    $decrypted = $filename[0].'.txt';
    shell_exec("echo $passphrase | gpg --no-tty --passphrase-fd 0 -o $decrypted -d $encrypted");
}