Php exec not working from browser

[PHP 4, PHP 5, PHP 7, PHP 8]

shell_exec — Execute command via shell and return the complete output as a string

Description

shell_exec[string $command]: string|false|null

Note:

On Windows, the underlying pipe is opened in text mode which can cause the function to fail for binary output. Consider to use popen[] instead for such cases.

Parameters

The command that will be executed.

Return Values

A string containing the output from the executed command, false if the pipe cannot be established or null if an error occurs or the command produces no output.

Note:

This function can return null both when an error occurs or the program produces no output. It is not possible to detect execution failures using this function. exec[] should be used when access to the program exit code is required.

Errors/Exceptions

An E_WARNING level error is generated when the pipe cannot be established.

Examples

Example #1 A shell_exec[] example

See Also

• exec[] - Execute an external program
• escapeshellcmd[] - Escape shell metacharacters

trev at dedicate.co.uk ¶

10 years ago

If you're trying to run a command such as "gunzip -t" in shell_exec and getting an empty result, you might need to add 2>&1 to the end of the command, eg:

Won't always work:
echo shell_exec["gunzip -c -t $path_to_backup_file"];

Should work:
echo shell_exec["gunzip -c -t $path_to_backup_file 2>&1"];

In the above example, a line break at the beginning of the gunzip output seemed to prevent shell_exec printing anything else. Hope this saves someone else an hour or two.

smcbride at msn dot com ¶

1 year ago

proc_open is probably a better solution for most use cases as of PHP 7.4.  There is better control and platform independence.  If you still want to use shell_exec[], I like to wrap it with a function that allows better control.

Something like below solves some problems with background process issues on apache/php.  It also

public function sh_exec[string $cmd, string $outputfile = "", string $pidfile = "", bool $mergestderror = true, bool $bg = false] {
  $fullcmd = $cmd;
  if[strlen[$outputfile] > 0] $fullcmd .= " >> " . $outputfile;
  if[$mergestderror] $fullcmd .= " 2>&1";
  if[$bg] {
    $fullcmd = "nohup " . $fullcmd . " &";
    if[strlen[$pidfile]] $fullcmd .= " echo $! > " . $pidfile;
  } else {
    if[strlen[$pidfile] > 0] $fullcmd .= "; echo $$ > " . $pidfile;
  }
  shell_exec[$fullcmd];
}

alexandre dot schmidt at gmail dot com ¶

6 years ago

To run a command in background, the output must be redirected to /dev/null. This is written in exec[] manual page. There are cases where you need the output to be logged somewhere else though. Redirecting the output to a file like this didn't work for me: