Perl 101 (Part 4) - Mind Games - Testing Times
( Page 6 of 10 )

Perl also comes with a bunch of operators that allow you to test the status of a file - for example, find out whether it exists, whether it's empty, whether it's readable or writable, and whether it's a binary or text file. Of these, the most commonly used operator is the "-e" operator, which is used to test for the existence of a specific file.

Here's an example which asks the user to enter the path to a file, and then returns a message displaying whether or not the file exists:

---

#!/usr/bin/perl

print "Enter path to file: ";
$path = <STDIN>;
chomp $path;

if (-e $path)
        {
        print "File exists!\n";
        }
else
        {
        print "File does not exist!\n";
        }

---

There are many more operators - here's a list of the most useful ones, together with an example which builds on the one above to provide more information on the file specified by the user.

---

OPERATOR:	TESTS WHETHER:
-----------------------------
-z		File exists and is zero bytes in size

-s		File exists and is non-zero bytes in size

-r		File is readable

-w		File is writable

-x		File is executable

-T		File is text

-B		File is binary

---

And here's a script that demonstrates how you could use these operators to obtain information on any file on your system:

---

#!/usr/bin/perl

# ask for file path and process it
print "Enter path to file: ";
$path = <STDIN>;
chomp $path;

# test for existence
if (-e $path)
	{
	print "File exists!\n";

# test for size
	if (-z $path)
		{
		print "File is empty.\n";
		}
	else
		{
		print "File is not empty.\n";
		}

# test for read access
	if (-r $path)
		{
		print "File is readable.\n";
		}
	else
		{
		print "File is not readable.\n";
		}

# test for write access
	if (-w $path)
		{
		print "File is writable.\n";
		}
	else
		{
		print "File is not writable.\n";
		}

# test for executable bit
	if (-x $path)
		{
		print "File is executable.\n";
		}
	else
		{
		print "File is not executable.\n";
		}

# test for whether file is text or binary
	if (-T $path)
		{
		print "File is a text file.\n";
		}
	elsif (-B $path)
		{
		print "File is a binary file.\n";
		}

	}
else
	{
	print "File does not exist!\n";
	}

---

And here's what it might look like:

---

Enter path to file: /usr/bin/mc
File exists!
File is not empty.
File is readable.
File is not writable.
File is executable.
File is a binary file.

---

This article copyright Melonfire 2000. All rights reserved.

>>> More Perl Articles          >>> More By Vikram Vaswani and Harish Kamath, (c) Melonfire