Exec with stdout / output redirected

You could have exec feature in your code / application. But if you need to exec with output redirected to a log file it will not work without pipes operations. But there is one trick - exec bash and provide your command with output redirected to a log as parameter to bash.

Syntax:

bash -c "command"

Example:

bash -c "ls -la"

Example with stdout redirected to a log:

bash -c "ls -la > log.txt"

In programming languages usually we have exec with several parameters:

• path - string
• args - array

java: Runtime.exec
php: pcntl_exec

So we need to prepare something like next:

• path = /bin/bash
• args:
  • arg1 = -c
  • arg2 = "command > log"     or     "command > log 2>&1"

Refer the PHP code below:

<?php
    /**
     * Execute an external program
     * @param string $path path to external program
     * @param array $args program arguments
     */
    function execute($path, $args) {
        return pcntl_exec($path, $args);
    }
  
    /**
     * Execute an external program with output redirected to log
     * @param string $path path to external program
     * @param array $args program arguments
     * @param string $log log file name
     */
    function execute_redir($path, $args, $log) {
        $path .= ' '.implode(' ', $args);
  
        $args = array();
        $args[] = '-c';
        $args[] = $path.' > '.$log.' 2>&1';
  
        $path = '/bin/bash';
        execute($path, $args);
    }
      
    // execute without output redirected
    //execute('/bin/ls', array('-la'));
      
    // execute with output redirected
    execute_redir('/bin/ls', array('-la'), 'log.txt');
?>