{if} statements in Smarty have much the same flexibility as PHP if statements, with a few added features for the template engine. Every {if} must be paired with a matching {/if}. {else} and {elseif} are also permitted. All PHP conditionals and functions are recognized, such as ||, or, &&, and, is_array(), etc.
If $security is enabled, only PHP functions from the IF_FUNCS array from$security_settings are allowed.
The following is a list of recognized qualifiers, which must be separated from surrounding elements by spaces. Note that items listed in [brackets] are optional. PHP equivalents are shown where applicable.
QualifierAlternatesSyntax ExampleMeaningPHP Equivalent==eq$a eq $bequals==!=ne, neq$a neq $bnot equals!=>gt$a gt $bgreater than><lt$a lt $bless than<>=gte, ge$a ge $bgreater than or equal>=<=lte, le$a le $bless than or equal<==== $a === 0check for identity===!notnot $anegation (unary)!%mod$a mod $bmodulous%is [not] div by $a is not div by 4divisible by$a % $b == 0is [not] even $a is not even[not] an even number (unary)$a % 2 == 0is [not] even by $a is not even by $bgrouping level [not] even($a / $b) % 2 == 0is [not] odd $a is not odd[not] an odd number (unary)$a % 2 != 0is [not] odd by $a is not odd by $b[not] an odd grouping($a / $b) % 2 != 0Example 7.15. {if} statements
{if $name eq 'Fred'} Welcome Sir. {elseif $name eq 'Wilma'} Welcome Ma'am. {else} Welcome, whatever you are. {/if} {* an example with "or" logic *} {if $name eq 'Fred' or $name eq 'Wilma'} ... {/if} {* same as above *} {if $name == 'Fred' || $name == 'Wilma'} ... {/if} {* parenthesis are allowed *} {if ( $amount < 0 or $amount > 1000 ) and $volume >= #minVolAmt#} ... {/if} {* you can also embed php function calls *} {if count($var) gt 0} ... {/if} {* check for array. *} {if is_array($foo) } ..... {/if} {* check for not null. *} {if isset($foo) } ..... {/if} {* test if values are even or odd *} {if $var is even} ... {/if} {if $var is odd} ... {/if} {if $var is not odd} ... {/if} {* test if var is divisible by 4 *} {if $var is div by 4} ... {/if} {* test if var is even, grouped by two. i.e., 0=even, 1=even, 2=odd, 3=odd, 4=even, 5=even, etc. *} {if $var is even by 2} ... {/if} {* 0=even, 1=even, 2=even, 3=odd, 4=odd, 5=odd, etc. *} {if $var is even by 3} ... {/if}Example 7.16. {if} with more examples
{if isset($name) && $name == 'Blog'} {* do something *} {elseif $name == $foo} {* do something *} {/if} {if is_array($foo) && count($foo) > 0} {* do a foreach loop *} {/if} 来源：http://www.smarty.net/docsv2/en/language.function.if.tpl