Database System Concepts
7th Edition
ISBN: 9780078022159
Author: Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher: McGraw-Hill Education
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![## Displaying Last n Lines of a File from the Command Line
### Introduction
Unix-based operating systems usually include a tool named `tail`. This tool displays the last 10 lines of a file whose name is provided as a command line argument.
### Task Overview
Write a program that provides the same behavior as `tail`, but with an added functionality: the user can specify how many lines to print from the terminal. The program should also display an appropriate error message if the file requested by the user does not exist or if the command line argument is omitted.
### Objective
To display the last n lines of a file whose name is provided as a command line argument.
### Instructions
- The program should accept a file name and the number of lines to display as inputs.
- Implement error handling to manage cases where:
- The file does not exist.
- No command line argument is provided.
### Note
You may need to pass a file as an argument when running the program. Make sure to have access to a sample file, the contents of which you want to print out.
**Example Code Structure:**
```python
import sys
def tail(filename, n=10):
try:
with open(filename, 'r') as file:
lines = file.readlines()
if len(lines) <= n:
print(''.join(lines))
else:
print(''.join(lines[-n:]))
except FileNotFoundError:
print(f"Error: The file '{filename}' does not exist.")
except IndexError:
print("Error: Please provide the filename as a command line argument.")
if __name__ == "__main__":
if len(sys.argv) < 2:
print("Usage: python tail.py FILENAME [N]")
else:
filename = sys.argv[1]
n = int(sys.argv[2]) if len(sys.argv) > 2 else 10
tail(filename, n)
```
This example demonstrates handling command line arguments in Python. Modify the approach based on the programming language you use. The error handling ensures that the user receives appropriate feedback in case of missing or incorrect inputs.](https://content.bartleby.com/qna-images/question/11ad9986-04b0-4336-8340-a3038312afe8/a5ecd008-a6f7-4f8f-a7d9-d5d56c75a72c/njyg8ma_processed.jpeg)
Transcribed Image Text:## Displaying Last n Lines of a File from the Command Line
### Introduction
Unix-based operating systems usually include a tool named `tail`. This tool displays the last 10 lines of a file whose name is provided as a command line argument.
### Task Overview
Write a program that provides the same behavior as `tail`, but with an added functionality: the user can specify how many lines to print from the terminal. The program should also display an appropriate error message if the file requested by the user does not exist or if the command line argument is omitted.
### Objective
To display the last n lines of a file whose name is provided as a command line argument.
### Instructions
- The program should accept a file name and the number of lines to display as inputs.
- Implement error handling to manage cases where:
- The file does not exist.
- No command line argument is provided.
### Note
You may need to pass a file as an argument when running the program. Make sure to have access to a sample file, the contents of which you want to print out.
**Example Code Structure:**
```python
import sys
def tail(filename, n=10):
try:
with open(filename, 'r') as file:
lines = file.readlines()
if len(lines) <= n:
print(''.join(lines))
else:
print(''.join(lines[-n:]))
except FileNotFoundError:
print(f"Error: The file '{filename}' does not exist.")
except IndexError:
print("Error: Please provide the filename as a command line argument.")
if __name__ == "__main__":
if len(sys.argv) < 2:
print("Usage: python tail.py FILENAME [N]")
else:
filename = sys.argv[1]
n = int(sys.argv[2]) if len(sys.argv) > 2 else 10
tail(filename, n)
```
This example demonstrates handling command line arguments in Python. Modify the approach based on the programming language you use. The error handling ensures that the user receives appropriate feedback in case of missing or incorrect inputs.
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