Thanks to Cory Marsh for pointing to this issue.

It is possible to receive php errors on the trigger expressions test page:

Parse error: syntax error, unexpected '{' in include/triggers.inc.php(2257) : eval()'d code on line 1

    Undefined variable: result [tr_testexpr.php:147 ? evalExpressionData() in include/triggers.inc.php:2259]
    Undefined variable: result [tr_testexpr.php:167 ? evalExpressionData() in include/triggers.inc.php:2259]

How to reproduce:

• open trigger expression test page with trigger function like {Zabbix server:agent.hostname.last()} (the value type of the item should be character, text or log)
• enter value

  {#DEF}*{hostname:mysql.primary_master.last($g=[`echo 41 > /tmp/h2.txt`];}#)}

• press [Test] button

Possible solutions:

1. to forbid character data for all value types
2. to rewrite trigger expression evaluation algorythm without using eval() function