#!/usr/bin/perl -w
#Experimenting with files

print "Enter filename:";
chomp($fname = <STDIN>);

## Open a file.  If unsuccessful, print an error message and quit.

open (FPTR,$fname) || die "Can't Open File: $fname\n";

# First Technique: "Slurping"
# This approach reads the ENTIRE file into memory 
# Caution... This is not a good method for BIG files!!!

@filestuff = <FPTR>;  #Read the file into an array
print "The number of lines in this file is ",$#filestuff + 1,"\n";
print @filestuff;

close (FPTR);         #Close the file

## Some other useful capabilities
## Testing file attributes:

print "Enter another filename:";
chomp($fname = <STDIN>);

if (-T $fname)   # Check if it's a textfile, and how old
   {
    print "File $fname is textfile. ";
    print "It was modified ", int(-M $fname), " days ago.\n";
    open (FPTR,$fname) || die "Sorry.  Can't Open File: $fname\n";
   }

elsif (-B $fname)   # Check if it's a binary file, and some other stuff
   {
    print "File $fname is executable.\n" if (-x $fname);
    print "This file is ", -s $fname, " bytes.\n";
    die "Since it is Binary file, we will not try to \"upcase\" this file.\n";
   }
else
   {die "File $fname is neither text nor binary, so it may not exist. \n" ;
   }


## Open a file for writing.  Note UNIX-like I/O redirection symbol, ">".

open (OUTFILE, ">upcase.txt") || die "Can't oupen output file.\n";

    
## Better approach for large files... Work with just current input line.

while (<FPTR>)  # While still input lines in the file...
  {
   print "1. ",$_;     # The symbol "$_" is the default variable, the current
                 #   input from file.  Note: "$_" is assumed if left out.

   tr/a-z/A-Z/;  # Translate all lower case letters to uppercase letters
                 #   in the default variable.
   
   print "2. ", $_;
   s/A/@/g;      # More substitutions:  All "A" chars become "@" signs.
   print"3. ", $_;
   s/UP/Down/g;  # All "UP" words are replaced by the string "Down" 
   print "4. ", $_;
   $pattern = '\sF(.*)L';  # Meaning of Regular Expression:
                           # \sF - starts with a <space> and capital F
                           # .*  - some stuff in between
                           # L  - Has a capital L in it

			   # The parentheses "mark" the stuff in between

   print "   Match value: ", $1, "\n" if (/$pattern/);; 

   s/$1/*/g if $_ =~ $pattern; # Substitute "*" for the marked pattern,
                               #  but anywhere within the line.
   print "5. ", $_, "\n";
   print OUTFILE $_;  # Print default variable to OUTFILE.
  }

close (FPTR);   # Close the other two files
close (OUTFILE);