Why is my Bash script failing to execute when called from PHP using `shell_exec`?

Executing Bash Commands from PHP: Troubleshooting Failed Script Execution

In this question, we encounter a PHP developer attempting to execute a bash script from PHP using shell_exec. The syntax used is:

<code class="php">$output = shell_exec("./script.sh var1 var2");</code>

However, the script fails to execute when this command is called.

To debug this issue, it's important to identify the cause of the failure. As the script executes successfully when running via the command line using ./script.sh var1 var2, the problem likely lies within the PHP code.

One common issue that can cause script execution failure is incorrect directory permissions or paths. PHP scripts often require the correct working directory to be set before executing external commands. To resolve this, the code can specify the correct directory using chdir before calling shell_exec.

The following snippet addresses this issue:

<code class="php">$old_path = getcwd();
chdir('/my/path/');
$output = shell_exec('./script.sh var1 var2');
chdir($old_path);</code>

In this example, we:

1. Store the current working directory in $old_path.
2. Change the working directory to '/my/path/' using chdir.
3. Execute the bash script using shell_exec.
4. Change back to the original working directory using chdir($old_path).

By ensuring that the correct directory is in place, this modified code should successfully execute the bash script from PHP.

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