Analysing text files to obtain statistics on their content 

You are to write a Perl program that analyses text files to obtain sta
+tistics on their content. The program should operate as follows: 

1) When run, the program should check if an argument has been provided
+. If not, the program should prompt for, and accept input of, a filen
+ame from the keyboard. 

2) The filename, either passed as an argument or input from the keyboa
+rd, should be checked to ensure it is in MS-DOS format. The filename 
+part should be no longer than 8 characters and must begin with a lett
+er or underscore character followed by up to 7 letters, digits or und
+erscore characters. The file extension should be optional, but if giv
+en is should be ".TXT" (upper- or lowercase). 

If no extension if given, ".TXT" should be added to the end of the fil
+ename. So, for example, if "testfile" is input as the filename, this 
+should become "testfile.TXT". If "input.txt" is entered, this should 
+remain unchanged. 

3) If the filename provided is not of the correct format, the program 
+should display a suitable error message and end at this point. 

4) The program should then check to see if the file exists using the f
+ilename provided. If the file does not exist, a suitable error messag
+e should be displayed and the program should end at this point. 

5) Next, if the file exists but the file is empty, again a suitable er
+ror message should be displayed and the program should end. 

6) The file should be read and checked to display crude statistics on 
+the number of characters, words, lines, sentences and paragraphs that
+ are within the file. 



I am very new to Perl and have managed to compile this code using exam
+ples from various books. Could anyone oversee this coding and see how
+ it could be improved. 

#!/usr/bin/perl 

use strict; 
use warnings; 

if ($#ARGV == -1) #no filename provided as a command line argument. 
{ 
print("Please enter a filename: "); 
$filename = <STDIN>; 
chomp($filename); 
} 
else #got a filename as an argument. 
{ 
$filename = $ARGV[0]; 
} 

#perform the specified checks 
#check if filename is valid, exit if not 
if ($filename !~ m^/[a-z]{1,7}\.TXT$/i) 
{ 
die("File format not valid\n");) 
} 

if ($filename !~ m/\.TXT$/i) 
{ 
$filename .= ".TXT"; 
} 

#check if filename is actual file, exit if it is. 
if (-e $filename) 
{ 
die("File does not exist\n"); 
} 

#check if filename is empty, exit if it is. 
if (-s $filename) 
{ 
die("File is empty\n"); 
} 

my $i = 0; 
my $p = 1; 
my $words = 0; 
my $chars = 0; 

open(READFILE, "<$data1.txt") or die "Can't open file '$filename: $!";
+ 

#then use a while loop and series of if statements similar to the foll
+owing 
while (<READFILE>) { 
chomp; #removes the input record Separator 
$i = $.; #"$". is the input record line numbers, $i++ will also work 
$p++ if (m/^$/); #count paragraphs 
$my @t = split (/\s+/); #split sentences into "words" 
$words += @t; #add count to $words 
$chars += tr/ //c; #tr/ //c count all characters except spaces and add
+ to $chars 
} 


#display results 
print "There are $i lines in $data1\n"; 
print "There are $p Paragraphs in $data1\n"; 
print "There are $words in $data1\n"; 
print "There are $chars in $data1\n"; 

close(READFILE);
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