Introduction to Perl programming

Perl is a high-level, general-purpose programming language that excels in text processing, system administration, web development, and more. Its flexibility and strong regular expression capabilities make it a popular choice for scripting tasks. This article introduces the basics of Perl programming, including an example script.

Basics of Perl

Running a Perl Script

To execute a Perl script, save the code in a file with a .pl extension (e.g., script.pl) and run it from the command line:

perl script.pl
    

Syntax Highlights

1. Shebang Line: Specify the interpreter.

   #!/usr/bin/perl
       

2. Comments: Use # for single-line comments.

   # This is a comment
       

3. Printing Output:

   print "Hello, World!\n";
       

Variables

Perl has three main variable types:

• Scalars: Single values (numbers, strings, etc.), prefixed by $.

  my $name = "Eva";
      my $age = 35;
      

• Arrays: Ordered lists, prefixed by @.

  my @colors = ("red", "green", "blue");
      

• Hashes: Key-value pairs, prefixed by %.

  my %capitals = ("France" => "Paris", "Japan" => "Tokyo");
      

Control Structures

• Conditional Statements:

  if ($age > 18) {
          print "You are an adult.\n";
      } else {
          print "You are a minor.\n";
      }
      

• Loops:

  for my $color (@colors) {
          print "$color\n";
      }
      

Example Script: Text File Analysis

This script reads a text file, counts the lines, words, and characters, and prints the results.

Script

#!/usr/bin/perl
    use strict;
    use warnings;
    
    # Check for file argument
    if (@ARGV != 1) {
        die "Usage: $0 <filename>\n";
    }
    
    my $filename = $ARGV[0];
    
    # Open the file
    open(my $fh, '<', $filename) or die "Could not open file '$filename': $!\n";
    
    # Initialize counters
    my ($line_count, $word_count, $char_count) = (0, 0, 0);
    
    # Process the file
    while (my $line = <$fh>) {
        $line_count++;
        $char_count += length($line);
        $word_count += scalar(split(/\s+/, $line));
    }
    
    close($fh);
    
    # Print results
    print "File: $filename\n";
    print "Lines: $line_count\n";
    print "Words: $word_count\n";
    print "Characters: $char_count\n";
    

Explanation

1. Input Validation: Ensures the script is called with a filename.
2. File Handling: Uses open and close for file operations.
3. Counters: Tracks lines, words, and characters.
4. Loop: Reads the file line by line, processing each line.

Running the Script

Save the script as file_analysis.pl and run it with a text file:

perl file_analysis.pl sample.txt
    

Conclusion

Perl is a powerful tool for scripting and data processing. Its concise syntax and robust text-handling capabilities make it an excellent choice for many tasks. This example demonstrates basic Perl features and encourages further exploration of its vast capabilities.