Webmaster in a Nutshell, Third Edition

Conditional Statements

Apache allows you to include only select portions of a server document using conditional statements. These conditional statements are based on the value of server-side variables initialized earlier using the SSI set command. The Apache flow-control statements allow you to effectively customize a document without adding more complex CGI programs to perform the same task.

There are four Apache flow-control statements:

<!--#if expr="expression" -->
<!--#elif expr="expression"-->
<!--#else-->
<!--#endif-->

Each works as you would expect from an ordinary scripting language. Note that each if must have a closing endif server-side statement. For example:

<!--#if expr="$myvar=activated" --> 
<B>The variable appears to be activated</B>
<!--#elif expr="$myvar=inactive"--> 
<B>The variable appears to be inactive</B>
<!--#else--> 
<B>The variable has an unknown value</B>
<!--#endif-->

Table 13-2 shows the allowed expressions, where the order of operations is as expected in a traditional programming language. Note that in some cases, var2 is allowed to be an egrep-based regular expression if it is surrounded by slashes (/) on both sides.

Table 13-2. XSSI conditional expressions

Expression	Meaning
var	True if the variable is not empty
var1=var2	True if the variables match
var1!=var2	True if the variables do not match
var1<var2	True if the first variable is less than the second
var1<=var2	True if the first variable is less than or equal to the second ...