Describe how to handle signals and traps in shell scripts.

Handling signals and traps in shell scripts allows you to respond to specific events or interruptions that occur during script execution. Signals are notifications sent to a process to indicate events such as a termination request or a user interrupt. Traps, on the other hand, are mechanisms used to capture and handle signals within a shell script. Let's explore how signals and traps can be utilized in shell scripting:

1. Understanding Signals:
Signals are represented by numbers and have unique meanings. Some commonly used signals in shell scripting are:
* SIGINT (2): Generated when the user interrupts a process using Ctrl+C.
* SIGTERM (15): Sent to request the termination of a process gracefully.
* SIGHUP (1): Sent when a terminal session is disconnected or closed.

A complete list of signals can be found by running the `kill -l` command in the shell.

2. Handling Signals with Traps:
Traps allow you to define actions to be taken when a signal is received during script execution. Here's an example of using a trap to handle the SIGINT signal:

```
bash`#!/bin/bash

cleanup() {
echo "Interrupt signal received. Cleaning up..."
# Add cleanup logic here
exit 1
}

trap cleanup SIGINT

# Rest of the script
# ...`
```
In this example, the `cleanup` function is defined to handle the cleanup actions when the SIGINT signal (interrupt signal) is received. The `trap` command is used to associate the `cleanup` function with the SIGINT signal. When the script receives the SIGINT signal, it will execute the `cleanup` function before exiting.

You can define trap handlers for multiple signals and have different actions for each one. For example:

```
bash`#!/bin/bash

cleanup() {
echo "Interrupt signal received. Cleaning up..."
# Add cleanup logic here
exit 1
}

terminate() {
echo "Termination signal received. Exiting..."
# Add termination logic here
exit 0
}

trap cleanup SIGINT
trap terminate SIGTERM

# Rest of the script
# ...`
```
In this modified example, both the SIGINT and SIGTERM signals are trapped. The `cleanup` function is associated with SIGINT, and the `terminate` function is associated with SIGTERM. When either of these signals is received, the corresponding function will be executed before the script exits.

Traps can also be used to ignore or override the default behavior of signals. For example, to ignore the SIGINT signal:

```
bash`#!/bin/bash

trap '' SIGINT

# Rest of the script
# ...`
```
In this case, the empty string `''` is assigned to the SIGINT signal, effectively ignoring it. The script will continue running even if the user interrupts with Ctrl+C.

Handling signals and traps in shell scripts provides a way to gracefully handle interrupts, perform cleanup actions, or customize the behavior of the script based on specific events. It helps ensure the script responds appropriately to external signals, improving reliability and usability.