Hey Amar, let's break down why your redirect isn't firing after running run_gen_execute_map.ksh, and fix it step by step.

First, Spot the Obvious Syntax Error #

Looking at your code, there's a missing closing double quote in your header call—this would cause a PHP parse error right off the bat:

header("location:cycle_task_actions.php); // Missing " at the end

Fix that first:

header("Location: cycle_task_actions.php");

Pro tip: While HTTP doesn't strictly require it, capitalizing Location and adding a space after the colon follows standard conventions.

Why the Redirect Still Fails (Even After Fixing Syntax) #

The core issue is that exec() can capture output from your KSH script (either stdout or stderr) and send it to the browser before your header() call. Once any output is sent, PHP can't modify HTTP headers anymore—this is a super common gotcha with header redirects.

Even adding & to run the script in the background doesn't prevent this, because PHP might still hold onto output from the command before it fully detaches.

Step-by-Step Fixes #

1. Redirect All KSH Script Output to Null
   Modify your exec() call to discard all output from the KSH script, so nothing leaks into PHP's response:

   exec("run_gen_execute_map.ksh > /dev/null 2>&1 &");
   

   • > /dev/null sends standard output (stdout) to the null device (discards it)
   • 2>&1 redirects standard error (stderr) to the same place as stdout
   • The final & ensures the script runs in the background, so PHP doesn't wait for it to finish before moving on

2. Eliminate Premature Output
   Check your PHP file for any accidental output before the header() call:

   • Leading/trailing spaces outside of <?php ?> tags
   • A Byte Order Mark (BOM) at the start of the file (common if you edited the file on Windows)
   • Any echo, print, or var_dump statements before the redirect

   If you can't track down hidden output, use output buffering to clear it:

   ob_start(); // Start buffering output at the very top of your file
   exec("run_gen_execute_map.ksh > /dev/null 2>&1 &");
   ob_end_clean(); // Discard all buffered output before sending headers
   header("Location: cycle_task_actions.php");
   exit;
   

3. Add exit After the Redirect
   Always stop execution immediately after sending the redirect header to prevent any additional code from running (which might generate output or interfere):

   header("Location: cycle_task_actions.php");
   exit; // or die();
   

Final Working Code #

Putting it all together, your code should look like this:

<?php
exec("run_gen_execute_map.ksh > /dev/null 2>&1 &");
header("Location: cycle_task_actions.php");
exit;
?>

内容的提问来源于stack exchange，提问作者Amar Shah