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Functions and statements which will check tainted string
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## Functions and Statements which will spread the tainted mark of a tainted string

Function/Statement | Since
--- | ---
= (assign) | 0.1.0
. (concat) | 0.1.0
"{$var}" (variable substitution) | 0.1.0
.= (assign concat) | 0.1.0
strval | 0.3.0
explode | 0.3.0
implode | 0.3.0
sprintf | 0.3.0
vsprintf | 0.3.0
trim | 0.4.0
rtrim | 0.4.0
ltrim | 0.4.0

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Functions and statements which will check tainted string
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PHP Manual