The perlsyn doc on statment modifiers says that a line such as my $var = 1 if $test; leads to an undefined behaviour: you don't know what happens to the variable if the condition evaluates to false.

Anyway in your case, even if you had written my $var; $var = $params->{test} if exists $params->{test}, you would still have the same result, because unless $params->{test} exists, you don't put any value in $test1.

A simple way to do what you want is to write:

my $i = shift;
my $params = shift;
my $test1 = $i; # $test1 is $i by default
$test1 = $params->{test} if exists $params->{test}; # change its value
+ when appropriate
[download]

You may be interested by the defined or operator (which would still lead to autovivification of the $params->{test} value in your case), and the ternary operator to solve problems similar to this one.

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