How does exit status and error handling work internally in Linux?

In Linux, every process that runs in the system has an exit status. This status is a numeric value returned by a process when it terminates, indicating whether it was successful or encountered an error. The exit status can be checked using the special variable `$?` in the shell.

The exit status is an integer between 0 and 255. By convention, an exit status of 0 indicates that the process completed successfully, while any non-zero value indicates an error occurred. Programs can define custom exit codes to represent different types of errors, allowing users to understand what went wrong when a process fails.

To handle errors effectively, scripts can use conditional statements to check the exit status of commands. This allows for proper error handling and can help ensure that subsequent steps in a script only run if previous steps were successful.

Here’s an example in PHP to demonstrate how to execute a shell command and check its exit status:

<?php $command = "ls -l /nonexistent_directory"; // This will fail $output = []; $return_var = 0; exec($command, $output, $return_var); if ($return_var !== 0) { echo "There was an error executing the command. Exit status: " . $return_var; } else { echo "Command executed successfully."; } ?>

exit status error handling Linux processes

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