PHP executes shell command print error message

$cmd  =  "rm 1.txt";//delete a nonexistent file, view the error message $res = doshell ($cmd); Var_dump ($res);//The function has no restrictions. Can be placed directly in the code using Function doshell ($cmd, $cwd =null) {     $descriptorspec  = array (         0 => array ("Pipe",  "R"),     // stdin        1 => array ("Pipe",  "w"),     // stdout        2 => array ( "Pipe",  "W")      // stderr    );//          $cmd  =  './test.sh ';  //  Replace with the shell script you want to execute      /*     *  return value      *       Returns the resource type that represents the process,  when you are finished, call the  proc_close ()   function to close the resource.   returns  false if it fails.      * cmd  the command to execute      * descriptorspec  an indexed array.      *       the key representation descriptor for the array, 0  represents the standard input (stdin), 1   indicates standard output (stdout),2  represents a standard error (STDERR)      *       Array element values represent  PHP  how these descriptors are routed to child processes.      *                   pipe  (the second element can be a: r  that transmits the read side of the pipeline to the process,w  the write end of the pipeline to the process),      *                      and  file (the second element is a file name).      * pipes     *       will be set to an indexed array,  where the element is a file pointer created by the executing program that corresponds to the  PHP  end of the pipeline.      * cwd     *       The initial working directory to execute the command.  Must be   absolute   path,  set this parameter to  NULL  indicates the use of the default (working directory of the current  PHP  process)       * env     *       environment variable used by the command to execute.   Setting this parameter to  NULL  means using the same environment variables as the current  PHP  process.      *     * */     $proc  =  proc_open ($cmd,  $descriptorspec,  $pipes,  $cwd,  null);     //   $proc is false, indicating command execution failure     if  ($proc  == false)  {         return false;        // do  sth with HTTP response    } else {          $stdout  = stream_get_contents ($pipes [1]);         fclose ($pipes [1]);         $stderr  = stream_get_contents ($pipes [2]);         fclose ($pipes [2]);          $status  = proc_close ($proc);  //  release proc     }     $data  = array (          ' stdout '  =>  $stdout,         ' stderr '  = >  $stderr,         ' retval '  =>  $status      );    return  $data;}

PHP executes shell command print error message