Operators

Perl has numerous operators (over 50 of them!) that perform operations on string and numberic values. Some operators will be familiar from algebra (like "+", to add two numbers together), while others are more esoteric (like the "." string concatenation operator).

Numeric & String Operators

The "." operator acts on strings. The "!" operator acts on strings and numbers. The rest act on numbers.

Operator	Description	Example	Result
.	String concatenate	'Teddy' . 'Bear'	TeddyBear
=	Assignment	$a = 'Teddy'	$a variable contains 'Teddy'
+	Addition	3+2	5
-	Subtraction	3-2	1
-	Negation	-2	-2
!	Not	!1	0
*	Multiplication	3*2	6
/	Division	3/2	1.5
%	Modulus	3%2	1
**	Exponentiation	3**2	9
<FILEHANDLE>	File input	<STDIN>	Read a line of input from standard input
>>	Right bit shift	3>>2	0 (binary 11>>2=00)
<<	Left bit shift	3<<2	12 (binary 11<<2=1100)
|	Bitwise OR	3|2	3 (binary 11|10=11
&	Bitwise AND	3&2	2 (binary 11&10=10
^	Bitwise XOR	3^2	1 (binary 11^10=01

Operator Precedence

2+3*4;    # evaluates to 14, multiplication has precedence over addition
(2+3)*4;  # evaluates to 20, parentheses force the precedence

Logical Operators

These operators compare strings or numbers, returning TRUE or FALSE:

Numeric Comparison		String Comparison
3 == 2	equal to	'Teddy' eq 'Bear'	equal to
3 != 2	not equal to	'Teddy' ne 'Bear'	not equal to
3 < 2	less than	'Teddy' lt 'Bear'	less than
3 > 2	greater than	'Teddy' gt 'Bear'	greater than
3 <= 2	less or equal	'Teddy' le 'Bear'	less than or equal
3 >= 2	greater than or equal	'Teddy' ge 'Bear'	greater than or equal
3 <=> 2	compare	'Teddy' cmp 'Bear'	compare
		'Teddy' =~ /Bear/	pattern match

The <=> and cmp operators return:

• -1 if the left side is less than the right side
• 0 if the left side equals the right side
• +1 if the left side is greater than the right side

File Operators

Perl has special file operators that can be used to query the file system. These operators generally return TRUE or FALSE.

Example:

print "Is a directory!\n" if -d '/usr/home'; print "File exists!\n" if -e '/usr/home/lstein/test.txt'; print "File is plain text!\n" if -T '/usr/home/lstein/test.txt';

There are many of these operators. Here are some of the most useful ones:

-e filename	file exists
-r filename	file is readable
-w filename	file is writable
-x filename	file is executable
-z filename	file has zero size
-s filename	file has nonzero size (returns size)
-d filename	file is a directory
-T filename	file is a text file
-B filename	file is a binary file
-M filename	age of file in days since script launched
-A filename	same for access time

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