How to Implement a Timeout Function in Shell Scripting with a Predefined Duration?

Timeout Function with a Predefined Duration

In shell scripting, it's useful to have a mechanism to terminate long-running tasks to avoid excessive waiting. The challenge faced here is to wrap a function within a timeout script, returning False if it exceeds a specified time limit.

One approach is to set an asynchronous timer that triggers a False response after a pre-defined interval. Fortunately, such a solution is achievable using signal handlers in the signal library (available on UNIX-based systems).

The process involves creating a custom decorator (@timeout) that leverages signal.alarm() to set an alarm for the desired time interval. Within the decorated function, when the alarm expires, a TimeoutError exception is raised, effectively interrupting the operation.

To incorporate this solution into your code, save the following code as timeout.py and import it:

import errno
import os
import signal
import functools

class TimeoutError(Exception):
    pass

def timeout(seconds=10, error_message=os.strerror(errno.ETIME)):
    def decorator(func):
        def _handle_timeout(signum, frame):
            raise TimeoutError(error_message)

        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            signal.signal(signal.SIGALRM, _handle_timeout)
            signal.alarm(seconds)
            try:
                result = func(*args, **kwargs)
            finally:
                signal.alarm(0)
            return result

        return wrapper

    return decorator

Now, within your application code, annotate any potentially long-running function with the @timeout decorator. For example:

from timeout import timeout

# Short timeout
@timeout(5)
def slow_function():
    # ...

# Default timeout
@timeout
def another_slow_function():
    # ...

# Customize timeout and error message
@timeout(30, error_message="Task timed out")
def yet_another_slow_function():
    # ...

This approach ensures that if a function takes longer than the specified timeout interval, it will raise a TimeoutError and return False, allowing you to handle unexpected delays gracefully.

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