Perl/PHP

Here is a table of Perl's string comparison operators with some examples to show you how they're used. For all cases, assume that $x = 'a'.

Comparison	String Operators	Example	Result
Equal to	eq	$x eq 'a'	true
Not equal to	ne	$x ne 'b'	true
Less than	lt	$x lt 'b'	true
Greater than	gt	$x gt 'b'	false
Less than or equal to	le	$x le 'b'	true
Greater than or equal to	ge	$x ge 'b'	false

Comparison and interpolation

By itself, comparison really isn't that exciting. Been there, done that, big yawn. However, because Perl uses these operators to decide how to interpret the value in a scalar variable, you do need to know how that happens. Basically, if you use the numeric operators to compare two scalars, then both the values are treated as numbers and then compared. If you use the string operators, then they're treated as strings and compared. So you see, knowing how Perl interpolates values is critical to understanding what will happen in conditional tests.

Converting numbers to strings

This one's easy: just use quotes. Having said that, I now need to clarify that once you do you can't always get the correct numeric value back from the string.

Sometimes underscores are used to make numbers easier to read (you can't use commas because they're reserved for separating lists):

$x = 1_000_000;

$x = 1_000_000;
$y = 1_000_000;

However, if

$x = 1_000_000;
$y = '1_000_000';

Converting strings to numbers

When Perl tries to figure out the numeric value of a string, things get a little more complicated. First, it only tries to find a number at the beginning of a string. If it doesn't find one, the whole string is considered to be zero. Therefore,

$x = "abc123";

Also, Perl will only look at the first number in the string, and stops after it finds it. That's why if

$x = "1_000";

$x = "10 20 30 40 50";

The same principles apply if you use decimal points in the string, such as "9.0". The value will returned as 9. Now, if you're trying to compare the numeric values of 9 to 9.0, they are going to pass as being equal. But since the string values of "9" and "9.0" are not equal, I need to bring this to your attention. It's important not to make assumptions when you're comparing strings to strings and numbers to numbers. You have to know the rules, and pay attention to them.

As mentioned previously, Perl will not convert binary, hexadecimal, or octal numbers into decimals. If you need to convert those numbers, use the hex() or oct() functions.

So how does all of this work?

Well, if you want to compare string values, use the string operators. Use numeric operators if you want to compare the numeric values.

Using the point made in the previous section, if

$x = 9;
$y = 9.0;

if($x == $y)
{
  # Returns true, because it's a numeric comparison
  # Numerically, 9 and 9.0 are equivalent
}

if($x eq $y)
{
  # Returns false because "9" is not the same string as "9.0"
  # Remember that because you're using a string comparison
  # operator, Perl is going to do the conversion for you.
}

if($x = $y)
{
  # Returns true because there's only one '=' sign
  # This assigns the value of 9.0 to $x
  # (Bang head on desk several times...)
}

Summary

So you see, the only complicated thing about all of this is remembering to use the right set of operators to compare values. Understanding the rules of interpolation is the real key to knowing how strings and numbers get converted back and forth. If you understand that, then the rest is easy.