How can command substitution be utilized in shell scripts? Provide an example.

Command substitution is a feature in shell scripting that allows you to execute a command and substitute its output as part of another command or assign it to a variable. It provides a convenient way to capture the result of a command and use it within your script.

There are two syntaxes for command substitution:

1. Using Backticks:

* The backtick (`) character is used for command substitution, enclosing the command whose output you want to capture.
* Example:
```
bash`# Assign the current date to a variable using command substitution
current_date=`date +%Y-%m-%d`
echo "Today's date is $current\_date"`
```
2. Using Parentheses:

* The dollar sign followed by parentheses (`$(command)`) is an alternative syntax for command substitution, providing improved readability and nesting capabilities.
* Example:
```
bash`# Assign the current time to a variable using command substitution
current_time=$(date +%H:%M:%S)
echo "The current time is $current\_time"`
```

Command substitution can be utilized in various ways within shell scripts:

1. Substituting Command Output:

* You can use command substitution to capture the output of a command and incorporate it into another command or operation.
* Example:
```
bash`# Count the number of files in the current directory
file_count=$(ls | wc -l)
echo "There are $file\_count files in the directory"`
```
2. Dynamically Generating Arguments:

* Command substitution allows you to dynamically generate command-line arguments based on the output of a command.
* Example:
```
bash`# Create a backup file with a timestamp
backup_file="backup\_$(date +%Y%m%d).tar.gz"
echo "Creating backup file: $backup\_file"`
```
3. Embedding Command Output in Text:

* You can embed the output of a command within text strings or messages.
* Example:
```
bash`# Display a customized greeting message using command substitution
username="John"
greeting="Hello, $(echo $username)! Welcome to our website."
echo $greeting`
```
4. Complex Operations and Calculations:

* Command substitution allows you to perform complex operations and calculations by capturing the output of intermediate commands and using it in subsequent steps.
* Example:
```
bash`# Calculate the sum of a list of numbers using command substitution
numbers="10 20 30 40 50"
sum=$(echo $numbers | tr ' ' '\n' | awk '{sum+=$1} END{print sum}')
echo "The sum is: $sum"`
```

Command substitution provides a flexible and powerful way to capture the output of commands and use it within shell scripts. It enables dynamic behavior, data manipulation, and integration with other commands and operations, enhancing the functionality and versatility of your scripts.