Introducing UNIX and Linux

Perl

Overview
Introduction
      Why yet another utility?
      Beginning Perl
      Invoking Perl
      Documentation on perl
      Perl Scripts
Variables
Input and output
      Files and redirection
      Pipes
      The DATA filehandle
Fields
Control structures
Predefined Perl
      Functions
      Modules
Regular expressions
      Single character translation
      String editing
Perl and the Kernel
Quality code
When do I use Perl?
Summary
Exercises

Answer to chapter 12 question 3

# Process the first argument
open(DATA, $ARGV[0]) || die "Cannot open data file";

# Initialise running total
$length=0.0;

# Data file must have at least one line
# @oldcoordinate holds the previous line, and
#  @coordinate the current line

if () {
  # Extract the fields in the first line into
  # the array @oldcoordinate
  @oldcoordinate = split;
} else {
  # Terminate if the data file is empty
  die "No data";
}

# Loop through the lines of the file
while () {
  # The current leg is calculated by
  # subtracting the new coordinated from
  # the old
  @coordinate = split;
  $x = $coordinate[0] - $oldcoordinate[0];
  $y = $coordinate[1] - $oldcoordinate[1];

  # Use Pythagoras' Theorem!
  $d = sqrt ( $x*$x + $y*$y);

  # Update the running total
  $length += $d;

  # The new line now becomes the previous
  # coordinate
  @oldcoordinate = @coordinate;
}

# Tidy up the open file handle
close (DATA);

# Finally, output the answer
printf "The journey length is %0.2f km.\n", $length;