5. Extended Examples

1. Example 01

Here are scripts in Bash, Perl, Ruby, and Python to find all .conf files on your computer.

1.1 Bash Script

You can use the find command in Bash to search for .conf files.

#!/bin/bash
# Find all .conf files on the system
find / -type f -name "*.conf" 2>/dev/null

• /: Search starting from the root directory.
• -type f: Look for files only (not directories).
• -name "*.conf": Match files with a .conf extension.
• 2>/dev/null: Suppress permission denied errors.

1.2 Perl Script

In Perl, you can use the File::Find module to recursively search for .conf files.

#!/usr/bin/perl
use strict;
use warnings;
use File::Find;

# Start search from the root directory
my $start_dir = '/';

# Subroutine to process each file found
sub find_conf_files {
    if (-f $_ && $_ =~ /\.conf$/) {
        print "$File::Find::name\n";
    }
}

# Use find to search for .conf files
find(\&find_conf_files, $start_dir);

• File::Find::find: Recursively finds all files in the directory.
• -f $_: Checks if the file exists.
• $_ =~ /\.conf$/: Regex match for .conf files.

1.3 Ruby Script

Ruby provides the Find module to traverse directories.

#!/usr/bin/env ruby
require 'find'

# Start searching from the root directory
start_dir = '/'

Find.find(start_dir) do |path|
  if File.file?(path) && path.end_with?('.conf')
    puts path
  end
end

• Find.find: Recursively searches from the specified directory.
• File.file?: Checks if the path is a file.
• end_with?('.conf'): Matches .conf file extensions.

1.4 Python Script

In Python, you can use the os and fnmatch modules to find .conf files.

#!/usr/bin/env python3
import os
import fnmatch

# Start searching from the root directory
start_dir = '/'

# Walk through all directories and files
for dirpath, dirnames, filenames in os.walk(start_dir):
    for filename in fnmatch.filter(filenames, '*.conf'):
        print(os.path.join(dirpath, filename))

• os.walk: Recursively traverses directories.
• fnmatch.filter: Matches files with the .conf extension.

---

1.5 Running the Scripts

1. Save each script in a separate file (e.g., find_conf.sh, find_conf.pl, find_conf.rb, find_conf.py).

2. Make each script executable (for Bash, Perl, and Ruby):

   chmod +x find_conf.sh
   chmod +x find_conf.pl
   chmod +x find_conf.rb

3. Run the scripts:

   • Bash: ./find_conf.sh
   • Perl: ./find_conf.pl
   • Ruby: ./find_conf.rb
   • Python: python3 find_conf.py

These scripts will recursively search your system for .conf files starting from the root directory (/). Depending on your system permissions, you may need to run them as root using sudo.

Example 02

Here’s a Perl subroutine that takes a file name and a search term as parameters, opens the given file, and prints all lines where the search term appears:

#!/usr/bin/perl
use strict;
use warnings;

# Subroutine to search for a term in a file
sub search_in_file {
    my ($filename, $search_term) = @_;

    # Open the file for reading
    open my $fh, '<', $filename or die "Could not open file '$filename': $!";

    # Loop through each line in the file
    while (my $line = <$fh>) {
        # Print the line if the search term is found
        if ($line =~ /\Q$search_term\E/) {
            print $line;
        }
    }

    # Close the file handle
    close $fh;
}

# Example usage of the subroutine
my $file = 'example.txt';       # Replace with your file path
my $term = 'search term';       # Replace with your search term
search_in_file($file, $term);

Explanation:

• sub search_in_file { ... }: Defines the subroutine.
• Parameters:
  • $filename: The name of the file to open.
  • $search_term: The term to search for in the file.
• open my $fh, '<', $filename or die ...: Opens the file in read mode (<). If the file cannot be opened, the program will terminate with an error message.
• while (my $line = <$fh>) { ... }: Reads the file line by line.
• \Q$search_term\E: Ensures any special characters in the search term are treated literally in the regular expression.
• print $line: Prints the line if the search term is found in it.
• close $fh: Closes the file after reading.

Usage:

1. Replace example.txt with the path to the file you want to search.
2. Replace 'search term' with the search term you’re looking for.

This script will print all lines from the specified file where the search term appears.

3. Example 03

Here are examples of programs in Python and Ruby that parse a .csv file, including functions to print the header and contents.

3.1 Python Program:

import csv

def print_header(filename):
    """Prints the header of the CSV file."""
    with open(filename, mode='r', newline='') as file:
        reader = csv.reader(file)
        header = next(reader)  # Get the first row as the header
        print("Header:", header)

def print_contents(filename):
    """Prints the contents of the CSV file."""
    with open(filename, mode='r', newline='') as file:
        reader = csv.reader(file)
        next(reader)  # Skip the header
        for row in reader:
            print(row)

# Example usage
csv_file = 'example.csv'  # Replace with your CSV file path
print_header(csv_file)
print_contents(csv_file)

3.2 Ruby Program

require 'csv'

def print_header(filename)
  """Prints the header of the CSV file."""
  CSV.foreach(filename).with_index do |row, index|
    if index == 0
      puts "Header: #{row.join(', ')}"
      break
    end
  end
end

def print_contents(filename)
  """Prints the contents of the CSV file."""
  CSV.foreach(filename).with_index do |row, index|
    next if index == 0  # Skip the header
    puts row.join(', ')
  end
end

# Example usage
csv_file = 'example.csv'  # Replace with your CSV file path
print_header(csv_file)
print_contents(csv_file)

Explanation:

• Python:

  • csv Module: Used for reading and writing CSV files.
  • print_header Function:
    • Opens the CSV file and reads the first row to print the header.
  • print_contents Function:
    • Reads the remaining rows and prints each row’s contents.

• Ruby:

  • csv Library: Standard library for handling CSV files.
  • print_header Function:
    • Uses CSV.foreach to iterate through the CSV file and prints the first row as the header.
  • print_contents Function:
    • Similar to print_header, but skips the first row and prints the remaining rows.

Usage:

1. Replace example.csv with the path to your CSV file in both programs.
2. Run the respective program in your Python or Ruby environment.

Both programs will print the header and the contents of the specified CSV file.