#!/usr/bin/perl -w
# This program experiments with simple matching operations

print "Enter a file name:";
chomp($fname = <STDIN>);     # File name is read from standard input (keyboard).
                             # Chomp removes any carriage returns from input

print "\nLooking for $fname in the following directory:\n";

$dir_list = `ls -l`;    # run the UNIX Command - assign output to a variable
print $dir_list,"\n";

### Simple Matches ###

# Common "if" approach at end of statement using MATCH operator "=~" 

print "Found file $fname in directory.\n" if $dir_list =~ $fname;


# Familiar "if-else" construction using NO-MATCH operator "!~"

if ($dir_list !~ $fname)
     { 
      print "Sorry... No $fname in this directory.\n\n";
     } 

else {
      print "Got a Match!\n\n";
     }

### Advanced Matching Capabilities ###

# Create an Array using the directory listing
@dir_array  = `ls -l`;

print "Here is the directory again:\n";
print @dir_array, "\n";

print "Here are the perl programs:\n";
$max_lines = $#dir_array;  #  The "$#" returns highest array index 

$pattern = '\s+(\w+\.+pl)\s';  #Define a pattern using "regular expressions"

# Meaning "\s+" - at least one or more spaces or tabs
#         "\w+" - at least one or more alpha-numeric characters 
#         "\.+" - a period or dot
#         "pl" - the proper "pl" extender
#         "\s" - a trailing space
$j=0;
for ($i=0; $i <= $max_lines; $i++) # Loop through all lines
{
    if ($dir_array[$i] =~ $pattern)
       {print $1, "\n";
        $perlprogs[$j] = $1;
        $j++;
       }
}
print "The program names are also stored in an array: ";
$, = ", ";
print @perlprogs;
print "\n";